Dampener system for a posterior stabilization system with a fixed length elongated member

ABSTRACT

Dynamic posterior stabilization systems are described. A dynamic posterior stabilization system may include bone fasteners and a dampener system. The dampener system may include a fixed length elongated member. The dampener system may also include one or more dampener sets. The dampener sets may provide resistance to movement of vertebrae coupled to the dynamic posterior stabilization system. In some embodiments, the elongated member has at least two portions having different diameters. The different portions interact with other portions of the dampener system to allow for compression of a dampener set. In some embodiments, the dampener system includes a sleeve coupled to the elongated member. In some embodiments, the dampener system includes a pair of washers coupled to the elongated member. The sleeve or the pair of washers allow the dampener system to be secured to a bone fastener.

BACKGROUND

1. Field of the Invention

Embodiments of the invention generally relate to functional spinalimplant assemblies for insertion into an intervertebral space betweenadjacent vertebrae of a human spine and reconstruction of the posteriorelements to provide stability, flexibility, and proper biomechanicalmotion. More specifically, embodiments relate to spinal stabilizationsystems that include one or more dynamic posterior stabilizationsystems.

2. Description of Related Art

The human spine is a complex mechanical structure including alternatingbony vertebrae and fibrocartilaginous discs that are connected by strongligaments and supported by musculature that extends from the skull tothe pelvis and provides axial support to the body. The intervertebraldiscs provide mechanical cushion between adjacent vertebral segments ofthe spinal column and generally include two basic components: thenucleus pulposus and the annulus fibrosis. The intervertebral discs arepositioned between two vertebral end plates. The annulus fibrosis formsthe perimeter of the disc and is a tough outer ring that binds adjacentvertebrae together. The end plates are made of thin cartilage overlyinga thin layer of hard cortical bone that attaches to the spongy,cancellous bone of a vertebra. The vertebrae generally include avertebral foramen bounded by the anterior vertebral body and the neuralarch, which consists of two pedicles that are united posteriorly by thelaminae. The spinous and transverse processes protrude from the neuralarch. The superior and inferior articular facets lie at the root of thetransverse process.

The spine is a flexible structure capable of a high degree of curvatureand twist in nearly every direction. The motion segment or functionalspinal unit (FSU) is the basic motion unit of the lumbar spine. Theanterior elements of the FSU include the vertebral bodies, theintervertebral disc, and the connecting soft tissues and ligaments. Theposterior elements of the FSU include the bony ring created by thepedicles and lamina, the facet joints, and the connecting soft tissuesand ligaments. The facet joints are located on both sides at thejunction of superior and inferior bony projections of the posteriorelements.

The total motion of the spine results from the cumulative motion of theindividual FSUs. Each motion segment allows rotational motion in threedirections (flexion-extension, lateral bending, and axial rotation) andtranslational motion in three directions (anterior-posterior,medial-lateral, and superior-inferior). The available motion isprimarily governed by the intervertebral disc, facet joints, andligaments. Typical maximum amounts of lumbar rotation are up to about17° of flexion-extension, 6° of lateral bending, and 3° of axialrotation. Moderate motions of the spine during everyday living mayresult in less than 10° of flexion-extension.

Translation of one vertebral body with respect to an adjacent vertebralbody can be up to a few millimeters during rotation. The quality of themotion is described by the shape of the motion segment moment-rotationcurve. The motion segment moment-rotation curve is the rotationalresponse of the FSU due to loading away from the center of rotation. Themoment-rotation curves are non-linear with an initial low stiffnessregion, followed by a higher stiffness region. The initial region ofhigh flexibility, where spinal motion is produced with less resistanceto bending moments, is typically referred to as the neutral zone.Typically, the neutral zone ranges from 10-50% of the total range ofmotion. The stiffness (Nm/deg) in the neutral zone is about 10-30% ofthe high stiffness region. Alterations to the FSU caused by surgicalintervention, degeneration, acute injury, or other factors are thoughtto change this non-linear behavior.

Genetic or developmental irregularities, trauma, chronic stress, anddegenerative wear can result in spinal pathologies for which surgicalintervention may be necessary. In cases of deterioration, disease, orinjury, an intervertebral disc, or a portion of the intervertebral disc,may be removed from the human spine during a discectomy.

After some discectomies, one or more non-dynamic intervertebral devicesmay be placed in the disc space to fuse or promote fusion of theadjacent vertebrae. During some procedures, fusion may be combined withposterior fixation to address intervertebral disc and/or facet problems.The fusion procedure (e.g., posterior lumbar interbody fusion) and theposterior fixation procedure may be performed using a posteriorapproach. The posterior fixation and non-dynamic intervertebral devicesmay cooperate to inhibit motion and promote bone healing. Fusing twovertebrae together results in some loss of motion. Fusing two vertebraetogether may also result in the placement of additional stress on one ormore adjacent functional spinal units. The additional stress may causedeterioration of an adjacent functional spinal unit that may result inthe need for an additional surgical procedure or procedures.

After some discectomies, a dynamic intervertebral device (DID) may beplaced in the disc space. The DID may allow for movement of adjacentvertebrae coupled to the DID relative to each other. U.S. Pat. No.4,863,477 to Monson, which is incorporated herein by reference,discloses a resilient dynamic device intended to replace the resilienceof a natural human spinal disc. U.S. Pat. No. 5,192,326 to Bao et al.,which is incorporated herein by reference, describes a prostheticnucleus for replacing just the nucleus portion of a human spinal disc.U.S. Patent Application Publication No. 2005/0021144 to Malberg et al.,which is incorporated herein by reference, describes an expandablespinal implant. Allowing for movement of the vertebrae coupled to thedisc prosthesis may promote the distribution of stress that reduces oreliminates the deterioration of adjacent functional spinal units.

An intervertebral device may be positioned between vertebrae using aposterior approach, an anterior approach, a lateral approach, or othertype of approach. A challenge of positioning a device between adjacentvertebrae using a posterior approach is that a device large enough tocontact the end plates and slightly expand the space must be insertedthrough a limited space. This challenge is often further heightened bythe presence of posterior osteophytes, which may cause “fish mouthing”of the posterior vertebral end plates and result in very limited accessto the disc. A further challenge in degenerative disc spaces is thetendency of the disc space to assume a lenticular shape, which mayrequire a larger implant than can be easily introduced without causingtrauma to adjacent nerve roots. The size of rigid devices that maysafely be introduced into the disc space is thereby limited. During somespinal fusion procedures using a posterior approach, two implants areinserted between the vertebrae. During some posterior procedures, one orboth facet joints between the vertebrae may be removed to provideadditional room for the insertion of a fusion device. Removal of thefacet may also allow for the removal of soft tissue surrounding thefacet (for example, the facet capsule) that work to resist posteriordistraction.

The anterior approach poses significant challenges as well. Though thesurgeon may gain very wide access to the interbody space from theanterior approach, this approach has its own set of complications andlimitations. The retroperitoneal approach usually requires theassistance of a surgeon skilled in dealing with the visceral contentsand the great vessels. The spine surgeon has extremely limited access tothe nerve roots and no ability to access or replace the facet joints.Complications of the anterior approach that are approach specificinclude retrograde ejaculation, ureteral injury, and great vesselinjury. Injury to the great vessels may result in massive blood loss,postoperative venous stasis, limb loss, or death. The anterior approachis more difficult in patients with significant obesity and may bevirtually impossible in the face of previous retroperitoneal surgery.

Despite the difficulties of the anterior approach, the anterior approachdoes allow for the wide exposure needed to place a large device. Inaccessing the spine anteriorly, one of the major structural ligaments,the anterior longitudinal ligament, must be completely divided. A largeamount of anterior annulus must also be removed along with the entirenucleus. Once these structures have been resected, the vertebral bodiesmay need to be over distracted to place the device within the disc spaceand restore disc space height. Failure to adequately tension theposterior annulus and ligaments increases the risk of device failureand/or migration. Yet in the process of placing these devices, theligaments are overstretched while the devices are forced into the discspace under tension. Over distraction can damage the ligaments and thenerve roots. The anterior disc replacement devices currently availableor in clinical trials may be too large to be placed posteriorly, and mayrequire over distraction during insertion to allow the ligaments to holdthem in position.

A facet joint or facet joints of a functional spinal unit may besubjected to deterioration, disease or trauma that requires surgicalintervention. Disc degeneration is often coupled with facetdegeneration, so that disc replacement only may not be sufficienttreatment for a large group of patients.

Facet degeneration may be addressed using a posterior approach. Thus asecond surgical approach may be required if the disc degeneration istreated using an anterior approach. The need to address facetdegeneration has led to the development of facet replacement devices.Some facet replacement devices are shown in U.S. Pat. Nos. 6,419,703 toFallin et al.; 6,902,580 to Fallin et al.; 6,610,091 to Reiley;6,811,567 to Reiley; and 6,974,478 to Reiley et al, each of which isincorporated herein by reference. The facet replacement devices may beused in conjunction with anterior disc replacement devices, but thefacet replacement devices are not designed to provide a common center ofrotation with the anterior disc replacement devices. The use of ananterior disc replacement device that has a fixed center of rotationcontrary to the fixed center of rotation of the facet replacement devicemay restrict or diminish motion and be counterproductive to the intentof the operation.

During some spinal stabilization procedures a posterior fixation systemmay be coupled to the spine. During some procedures, posterior fixationsystems may be coupled to each side of the spine. The posterior fixationsystems may include elongated members that are coupled to vertebrae byfasteners (e.g., hooks and screws). One or more transverse connectorsmay be connected to the posterior fixation systems to join and stabilizethe posterior fixation systems.

During some spinal stabilization procedures, dynamic posteriorstabilization systems may be used. U.S. Patent Publication Nos.2005/0182409 to Callahan et al.; 2005/0245930 to Timm et al.; and2006/0009768 to Ritland, each of which is incorporated herein byreference, disclose dynamic posterior stabilization systems.

During some spinal stabilization procedures, a dynamic interbody deviceor devices may be used in conjunction with one or more dynamic posteriorstabilization systems. U.S. Patent Publication No. 2006/0247779 toGordon et al., and U.S. patent application Ser. No. 11/655,724 to Landryet al., each of which is incorporated herein by reference, disclosedynamic interbody devices and dynamic posterior stabilization systemsthat may be used together to stabilize a portion of a spine.

A portion of the load applied to a spine of a patient may apply shearforces to dynamic interbody devices positioned between vertebrae. Insome spinal stabilization systems, shear forces applied to the dynamicinterbody devices are resisted by rod and pedicle screw constructs. Theshear forces may apply large moments to the pedicle screws through therods that result in undesired loosening of the pedicle screws. In someembodiments, the pedicle screw and rod constructs are relatively massiveconstructs to accommodate applied shear loads without loosening.

The width of fusion devices or dynamic devices that are installed usinga posterior approach may be limited by the available insertion spaceand/or the need to limit retraction of neural structures exiting thevertebrae being stabilized. Subsidence of the lower vertebra caused by afusion device or dynamic device inserted using a posterior approach hasbeen noted in some patients. Subsidence may be due to small contact areabetween the vertebra and the device and/or by limited or no contact ofthe device over cortical bone surrounding the end plate of the vertebra.The contact surfaces of many fusion devices and/or dynamic interbodydevices that are inserted using posterior approaches have substantiallythe same contact area against the upper vertebra and the lower vertebrabeing stabilized.

Prosthetic replacement of the intervertebral disc accompanied by removalof the facet joints may require a dynamic stabilization system thatreplicates the physiological function of the removed or replacedstructures. Dynamic stabilization devices are typically attached to orplaced between the posterior elements of adjacent spinal units. A largenumber of dynamic stabilization devices have been previously proposed toprotect the spine from abnormal motion or loading, but it would be agreat advance in the art to provide a dynamic stabilization system thatphysiologically controls the pattern and magnitude of motion.

SUMMARY

In an embodiment, a posterior stabilization system may be secured to afirst vertebra and a second vertebra of a human spine to stabilize thevertebrae and provide resistance to movement of the vertebrae relativeto each other. The posterior stabilization system may include bonefastener and a dampener system.

In an embodiment, the dampener system comprises a fixed length elongatedmember, a dampener set, and an offset member. The fixed length elongatedmember comprises a first portion configured to couple to a first bonefastener, a second portion having a first diameter, and a third portionhaving a diameter less than the diameter of the second portion. Thedampener set is coupled to the second portion of the elongated member.The offset member is coupled to the elongated member and is configuredto couple to a second bone fastener.

In an embodiment, the dampener system comprises a fixed length elongatedmember, a first stop coupled to the elongated member, a second stopcoupled to the elongated member, a first dampener set positioned on theelongated member, a second dampener set positioned on the elongatedmember, and a member positioned between the first dampener set and thesecond dampener set. The member is configured to couple to a second bonefastener. Travel of the first dampener set on the elongated member islimited by the first stop, and travel of the second dampener set on theelongated member is limited by the second stop.

In an embodiment, the dampener system comprises a fixed length elongatedmember, a frame coupled to the elongated member, a first dampener setcoupled to the elongated member, a second dampener set coupled to theelongated member, and a slide coupled to the elongated member betweenthe first dampener set and the second dampener set. The elongated memberincludes a portion configured to couple to a first bone fastener. Theframe includes a portion configured to couple to a second bone fastener.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will become apparent to thoseskilled in the art with the benefit of the following detaileddescription and upon reference to the accompanying drawings in which:

FIG. 1 depicts embodiments of dynamic interbody devices positionedbetween vertebrae.

FIG. 2 depicts a rear view of dynamic interbody device embodiments.

FIG. 3 depicts a front view of the first member of a dynamic interbodydevice embodiment.

FIG. 4 depicts a side view of the first member of the dynamic interbodydevice embodiment.

FIG. 5 depicts a top view of the first member of the dynamic interbodydevice embodiment.

FIG. 6 depicts a front view of the second member of the dynamicinterbody device embodiment.

FIG. 7 depicts a side view of the second member of the dynamic interbodydevice embodiment.

FIG. 8 depicts a top view of the second member of the dynamic interbodydevice embodiment.

FIG. 9 depicts a bottom view of the second member of the dynamicinterbody device embodiment.

FIG. 10 depicts a perspective view of the second member of a dynamicinterbody device embodiment.

FIG. 11 depicts a perspective view of the third member of a dynamicinterbody device embodiment.

FIG. 12 depicts embodiments of dynamic interbody devices positionedbetween vertebrae.

FIG. 13 depicts the posterior end of an embodiment of a dynamicinterbody device.

FIG. 14 depicts a rear view of an embodiment of a pair of dynamicinterbody devices.

FIG. 15 depicts a bottom view of an embodiment of a pair of dynamicinterbody devices.

FIG. 16 depicts a side view of an embodiment of the first member of adynamic interbody device.

FIG. 17 depicts a perspective view of an embodiment of the second memberof a dynamic interbody device that emphasizes the bottom of the secondmember.

FIG. 18 depicts a perspective view of an embodiment of the second memberof a dynamic interbody device that emphasizes the top of the secondmember.

FIG. 19 depicts a perspective view of an embodiment of the third memberof a dynamic interbody device that emphasizes the bottom of the thirdmember.

FIG. 20 depicts a perspective view of an embodiment of the third memberof a dynamic interbody device that emphasizes the top of the thirdmember.

FIG. 21 depicts a perspective view of an embodiment of a dynamicinterbody device.

FIG. 22 depicts a side view of a first member of the dynamic interbodydevice depicted in FIG. 21.

FIG. 23 depicts a top view of the first member of the dynamic interbodydevice depicted in FIG. 21.

FIG. 24 depicts a front view of the first member of the dynamicinterbody device depicted in FIG. 21.

FIG. 25 depicts a side view of the second member of the dynamicinterbody device depicted in FIG. 21.

FIG. 26 depicts a top view of the second member of the dynamic interbodydevice depicted in FIG. 21.

FIG. 27 depicts a perspective view of the third member of the dynamicinterbody device depicted in FIG. 21.

FIG. 28 depicts a perspective view of an embodiment of a posteriorstabilization system.

FIG. 29 depicts an exploded perspective view of an embodiment of a bonefastener.

FIG. 30 depicts a perspective view of an embodiment of a bone fastener.

FIG. 31 depicts a perspective view of an embodiment of a bone fastener.

FIG. 32 depicts a plot of stress versus strain for the compression ofsilicone dampeners together with estimated stress-strain behaviorrequired by the dampeners to allow for normal physiological motion of areconstructed functional spinal unit.

FIG. 33 depicts a plot of normalized load versus number of compressioncycles for 70 durometer silicone elastomer at 20% or 40% strain.

FIG. 34 depicts a plot of plot of normalized length versus number ofcompression cycles for 70 durometer silicone elastomer at 20% or 40%strain.

FIG. 35 depicts a cross-sectional representation of a portion of anembodiment of a dynamic posterior stabilization system.

FIG. 36A depicts a cross section of a dampener set embodiment formed ofa two concentric cylinders.

FIG. 36B depicts a plot of force versus displacement for simulatedcompression of the dampener set depicted in FIG. 36A.

FIG. 37A depicts a cross section of a dampener set embodiment formed ofa two concentric cylinders.

FIG. 37B depicts a plot of force versus displacement for simulatedcompression of the dampener set depicted in FIG. 37A.

FIG. 38 depicts a side view representation of a portion of an embodimentof a dynamic posterior stabilization system.

FIG. 39 depicts a perspective view of an embodiment of a single smalldampener used to form dampener sets depicted in FIG. 38.

FIG. 40A depicts a cross section of a dampener set embodiment formed oflarge and small diameter sections.

FIG. 40B depicts a plot of force versus displacement for simulatedcompression of the dampener set depicted in FIG. 40A.

FIG. 41 depicts a cross-sectional representation of a dampener setembodiment with fillets and chamfered ends.

FIG. 42 depicts a side view representation of a portion of an embodimentof a dynamic posterior stabilization system where the dampener sets areformed of a number of segments.

FIG. 43 depicts a perspective view of an embodiment of a barrel shapeddampener set.

FIG. 44 depicts a cross-sectional representation of a plurality ofstacked conical washers that may be used as a dampener set of a dynamicposterior stabilization system.

FIG. 45 depicts an exploded view of an embodiment of an in-line,isolated dual dampener system.

FIG. 46 depicts an exploded view of an embodiment of a lateral offset,isolated dual dampener system.

FIG. 47 depicts a perspective view of an embodiment of a medial offsetmember that may be used to form a dampener system that is positionedmedial to a second bone fastener of a dynamic posterior stabilizationsystem.

FIG. 48 depicts a perspective view of an embodiment of a sleeve that maybe used to form an in-line dampener system.

FIG. 49 depicts a cross-sectional representation of an embodiment of adampener system.

FIG. 50 depicts a top view of a dampener system embodiment.

FIG. 51 depicts an embodiment of a dynamic posterior stabilizationsystem coupled to vertebrae with the dampener sets positioned in anon-inverted orientation.

FIG. 52 depicts embodiments of dynamic posterior stabilization systemscoupled to vertebrae with the dampener sets positioned in an invertedorientation.

FIG. 53 depicts an embodiment of a two level dynamic posteriorstabilization system.

FIG. 54 depicts an embodiment of a side by side dampener system.

FIG. 55 depicts a perspective view of an embodiment of a dampener systemthat spans across a vertebra.

FIG. 56 depicts a perspective view of an embodiment of a dynamicposterior stabilization system with an in-line, partially shared dualdampener system in a neutral position.

FIG. 57 depicts an exploded view of an embodiment of an in-line,partially shared dual dampener system.

FIG. 58 depicts a perspective view of an embodiment of a dynamicposterior stabilization system with a first dampener set of an in-line,partially shared dual dampener system in compression.

FIG. 59 depicts a perspective view of an embodiment of a dynamicposterior stabilization system with a first dampener set and a seconddampener set of an in-line, partially shared dual dampener system incompression.

FIG. 60 depicts a perspective view of an embodiment of an in-line,partially shared dual dampener system.

FIG. 61 depicts an exploded view of the in-line, partially shared dualdampener system depicted in FIG. 60.

FIG. 62 depicts a perspective view of an embodiment of an offset,partially shared dual dampener system with an external frame.

FIG. 63 depicts a cross-sectional representation of an embodiment of anoffset, partially shared dual dampener system with an external frame.

FIG. 64 depicts a front view of an embodiment of an in-line partiallyshared dual dampener system in a neutral position.

FIG. 65 depicts a side view of an embodiment of an in-line partiallyshared dual dampener system with the first dampener set compressed.

FIG. 66 depicts a side view of an embodiment of an in-line partiallyshared dual dampener system with the first dampener set and the seconddampener set compressed.

FIG. 67 depicts a perspective view of a dynamic posterior stabilizationsystem with an offset, single dampener system in a neutral position.

FIG. 68 depicts an exploded view of an offset, single dampener system.

FIG. 69 depicts a perspective view of a dynamic posterior stabilizationsystem compressed as if vertebrae coupled to the system were subjectedto extension and/or lateral bending towards the side that the system iscoupled to.

FIG. 70 depicts a perspective view of a dynamic posterior stabilizationsystem compressed as if vertebrae coupled to the system were subjectedto flexion and/or lateral bending away from the side that the system iscoupled to.

FIG. 71 depicts a perspective view of an embodiment of an offset, singledampener system with an external frame.

FIG. 72 depicts a cross-sectional representation of an embodiment of anoffset, single dampener system with an external frame.

FIG. 73 depicts a perspective view of an embodiment of a single dampenersystem in a neutral position.

FIG. 74 depicts an exploded view of the single dampener system depictedin FIG. 73.

FIG. 75 depicts a representation of a dynamic interbody device and aposterior stabilization system coupled to vertebrae.

FIG. 76 depicts a representation of taps positioned in a lower vertebraduring a spinal stabilization procedure.

FIG. 77 depicts a perspective view of an embodiment of an expandabletrial.

FIG. 78 depicts a perspective view of an end portion of the expandabletrial with the movable plate lifted from the base plate.

FIG. 79 depicts a perspective view of the expandable trial thatemphasizes the top of the expandable trial.

FIG. 80 depicts a perspective view of an embodiment of a guide.

FIG. 81 depicts a top view of the guide with the guide release in afirst position.

FIG. 82 depicts a top view of the guide with the guide release in asecond position.

FIG. 83 depicts a perspective view of an embodiment of an insertionbridge.

FIG. 84 depicts a front view of the insertion bridge.

FIG. 85 depicts a perspective view of the insertion bridge coupled toguides and expandable trials.

FIG. 86 depicts a perspective view of a bar assembly coupled to theinsertion bridge, guides, and expandable trials.

FIG. 87 depicts a perspective view of a rod connector attached to thetap and the rod of the bar assembly.

FIG. 88 depicts a perspective view of a keel guide and drill duringformation of a keel opening in a vertebra.

FIG. 89 depicts a perspective view of an embodiment of an insertioninstrument.

FIG. 90 depicts a perspective view of the lower vertebra with insertioninstruments placing the dynamic interbody devices at a desired position.

FIG. 91 depicts a perspective representation of an embodiment of asupport frame coupled to taps positioned in the lower vertebra.

FIG. 92 depicts a perspective view of an embodiment of a first guide fora bridge assembly.

FIG. 93 depicts a perspective view of an embodiment of an expandabletrial.

FIG. 94 depicts a representation of expandable trials positioned againstthe lower vertebra during the dynamic interbody device insertionprocedure.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Thedrawings may not be to scale. It should be understood, however, that thedrawings and detailed description thereto are not intended to limit theinvention to the particular form disclosed, but to the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the present invention as definedby the appended claims.

DETAILED DESCRIPTION

A “functional spinal unit” generally refers to a motion segment of aspine. The functional spinal unit may include two vertebrae, anintervertebral disc between the vertebrae, and the two facet jointsbetween the vertebrae. An “artificial functional spinal unit” refers toa functional spinal unit where one or more of the components of thefunctional spinal unit are replaced by implants or devices that permitat least some motion of the spine. At least a portion of theintervertebral disc and/or one or both of the facet joints may bereplaced by implants or devices during a spinal stabilization procedure.

As used herein, “coupled” includes a direct or indirect joining ortouching unless expressly stated otherwise. For example, a first memberis coupled to a second member if the first member contacts the secondmember, or if a third member is positioned between the first member andthe second member.

A “dynamic interbody device” generally refers to an artificialintervertebral implant that allows for flexion/extension, lateralbending and/or axial rotation of vertebrae coupled to the device. Thedynamic interbody device may replace a portion or all of anintervertebral disc. In some embodiments, a pair of dynamic interbodydevices are installed during a spinal stabilization procedure. In someembodiments, one or more dynamic interbody devices are installed using aposterior approach. In other embodiments, a dynamic interbody device maybe installed using an anterior approach or other type of approach. Insome embodiments, one or more dynamic interbody devices are placed in adisc space between vertebrae, and at least one posterior stabilizationsystem is coupled to the vertebrae. In some embodiments, one or moredynamic interbody devices are placed in the disc space without couplinga posterior stabilization system to the vertebrae.

In some embodiments, the dynamic interbody device is a bimodal device.Bimodal refers to a device that has at least two separate curvedsurfaces to accommodate flexion/extension with lateral bending and/oraxial rotation.

Dynamic interbody devices may have surfaces that contact vertebrae. Insome embodiments, a surface of the dynamic interbody device thatcontacts a vertebra may include one or more keels, protrusions, and/orosteoconductive/osteoinductive layers or coatings. A keel of the dynamicinterbody device may be positioned in a channel formed in a vertebra.The channel may be formed in the vertebra so that the dynamic interbodydevice will be positioned at a desired location when inserted into thepatient. Protrusions of the dynamic interbody device may penetrate anendplate of the vertebra to secure the dynamic interbody device to thevertebra. An osteoconductive/osteoinductive layer may promote bonegrowth that secures the dynamic interbody device to the vertebra. Theosteoconductive/osteoinductive layer may include, but is not limited toa scaffold, a roughened surface, a surface treated with a titaniumplasma spray, bone morphogenic proteins, and/or hydroxyapatite. Aroughened surface may be formed by chemical etching, by surfaceabrading, by shot peening, by an electrical discharge process, and/or byembedding particles in the surface.

An anterior end of a dynamic interbody device may have a height that isgreater than the height of a posterior end of the dynamic interbodydevice. The difference in heights between the anterior end and theposterior end of the dynamic interbody device may provide the patientwith a desired amount of lordosis. Dynamic interbody devices thatprovide different amounts of lordosis may be provided in an instrumentkit supplied for a spinal stabilization procedure. For example, theinstrument kit for a posterior spinal stabilization procedure mayinclude pairs of dynamic interbody devices that establish 0°, 3°, 6°,9°, 12° or 15° of lordosis. Other dynamic interbody device lordosisangles or lordosis angle ranges may be provided. The amount of lordosisprovided by a dynamic interbody device may be printed or etched on avisible surface of the dynamic interbody device. Other information mayalso be printed or etched on the visible surface of the dynamicinterbody device. Such information may include dimension information(e.g., length, width, and/or height) and whether the dynamic interbodydevice is to be installed on the left side of the patient or the rightside of the patient.

In some embodiments, one or more dynamic interbody devices are installedin a disc space formed between vertebrae during a spinal stabilizationprocedure. The shape and/or size of a dynamic interbody device maydepend on a number of factors including surgical approach employed forinsertion, intended position in the spine (e.g., cervical or lumbar),and patient anatomy. A dynamic interbody device for the lumbar spine mayhave a height that is less than about 22 mm. Several sizes of interbodydevices may be provided in the instrument kit for the spinalstabilization procedure. In an embodiment, dynamic interbody deviceshaving heights of 6 mm, 8 mm, 10 mm, 12, mm, 14 mm, 16 mm, 18 mm, and 20mm are provided in the instrument kit for the spinal stabilizationprocedure. In an embodiment, dynamic interbody devices having heights of7 mm, 8 mm, 9 mm, 10 mm, 12 mm and 14 mm are provided. Other sizesand/or different height ranges of dynamic interbody devices may beprovided in the instrument kit for the spinal stabilization procedure.The dynamic interbody devices may include indicia indicating the heightof the spinal stabilization devices.

The dynamic interbody devices may allow for flexion/extension. Thedynamic interbody device may allow for a maximum of about 20° of flexionfrom the neutral position. The dynamic interbody device may be designedso that the dynamic interbody device has a smaller or a larger maximumangle of flexion from the neutral position. In some embodiments, thedynamic interbody device allows for a maximum of about 7° of flexionfrom the neutral position. In some embodiments, the maximum amount offlexion allowed by the dynamic interbody device is substantially thesame as the maximum amount of extension allowed by the dynamic interbodydevice. In some embodiments, the maximum amount of flexion allowed bythe dynamic interbody device is different from the maximum amount ofextension. For example, an embodiment of a dynamic interbody deviceallows for a maximum of about 15° of flexion and a maximum of about 10°of extension.

The total flexion-extension range of motion may vary with implantheight. Shorter dynamic interbody devices may have smaller ranges ofmotion than taller dynamic interbody devices. For example, a 7 mmdynamic interbody device may have a flexion-extension range of motion ofabout 17°, and a 14 mm dynamic interbody device may have aflexion-extension range of motion of about 23°. The minimum desirablerange of motion may be ±2.5° since the prevalence of adjacent leveldegeneration after total disc replacement has been shown to be lower inpatients with greater than 5° of motion. The 7 mm dynamic interbodydevice with the flexion-extension range of motion of about 17° may beable to accommodate an angle between adjacent vertebral body endplatesof about 11.5° without additional built in lordotic angle. The 14 mmdynamic interbody device with the flexion-extension range of motion ofabout 23° may be able to accommodate an angle between adjacent vertebralbody endplates of about 17.5° without additional built in lordoticangle. Such dynamic interbody devices may allow for sufficient lordoticalignment since the intervertebral body angles are approximately 8.5° atthe L3-L4 level, 13° at the L4-L5 level, and 14.5° at the L5-S1 level.

The dynamic interbody device may allow for up to about 5° of axialrotation of vertebrae coupled to the dynamic interbody device (e.g.±2.5° of rotation from a neutral position). The dynamic interbody devicemay allow for more or less axial rotation. In an embodiment, the dynamicinterbody device allows for about ±1.5° of axial rotation of vertebraecoupled to the dynamic interbody device from a neutral position.

The dynamic interbody device may allow for up to about 10° of lateralbending of vertebrae coupled to the dynamic interbody device (e.g. ±5°of lateral bending from a neutral position). The dynamic interbodydevice may allow for more or less lateral bending. In an embodiment, thedynamic interbody device allows for about ±3° of lateral bending ofvertebrae coupled to the dynamic interbody device from a neutralposition.

The dynamic interbody device may allow for coupled lateral bending andaxial rotation so that axial rotation causes some lateral bending andlateral bending causes some axial rotation. The dynamic interbody devicemay be formed so that a set amount of lateral bending results in a setamount of axial rotation. For example, 1° of lateral bending results inabout 0.5° of axial rotation (i.e. a 2:1 ratio of lateral bending toaxial rotation). A 4:1, 3:1, 2.5:1, 2:1, 1.5:1, 1:1 or other ratio oflateral bending to axial rotation may be set for the dynamic interbodydevices. In some embodiments, dynamic interbody devices may be designedto be positioned between two particular vertebrae (e.g., between L4 andL5, between L3 and L4, etc.). The ratio of lateral bending to axialrotation may be selected mimic the natural ratio of lateral bending toaxial rotation for normal vertebrae of the same level.

In some embodiments, a pair of dynamic interbody devices may beinstalled between two vertebrae to establish all or a portion of aspinal stabilization system. Each dynamic interbody device of the pairof dynamic interbody devices may be installed using a posteriorapproach.

In some embodiments, a single dynamic interbody device may be positionedin a disc space between vertebrae. The use of a single dynamic interbodydevice may avoid the need to have left oriented and right orienteddynamic interbody devices. The single dynamic interbody device may beinstalled using an anterior approach, a posterior approach, or adifferent type of approach. Single dynamic interbody devices insertedusing an anterior approach may be installed using installationprocedures known in the art. The coupled axial rotation/lateral bendingof the anterior dynamic interbody device includes the functionality ofthe facet joints. One or both of the facets may be removed using asimple minimally invasive procedure without the need to install aposterior stabilization system.

As used herein a “dynamic posterior stabilization system” generallyrefers to an apparatus used to replace or supplement a facet joint whileallowing for both dynamic resistance and at least some motion of thefirst vertebra to be stabilized relative to the second vertebra to bestabilized. The first vertebra and the second vertebra may be vertebraeof a functional spinal unit. In some embodiments, bone fasteners of thedynamic posterior stabilization system are secured to the first vertebraand the second vertebra. In some embodiments, a bone fastener of thedynamic posterior stabilization system may be coupled to a vertebraadjacent to the vertebrae of the functional spinal unit beingstabilized. The bone fasteners may be coupled to lamina, pedicles,and/or vertebral bodies of the vertebrae. In some embodiments, dynamicposterior stabilization systems may be positioned in three or morevertebrae to form a multi-level stabilization system.

The dynamic posterior stabilization system may replace or supplement anormal, damaged, deteriorated, defective or removed facet joint. Thedynamic posterior stabilization system may include bone fasteners, anelongated member, and at least one bias member. The bias member mayprovide little or no initial resistance to movement of a first vertebracoupled to the system relative to a second vertebra coupled to thesystem. Resistance to additional movement of the first vertebra relativeto the second vertebra may increase. The increasing resistance providedby the bias member may mimic the behavior of a normal functional spinalunit. The dynamic posterior stabilization system may stabilize thevertebrae, limit the range of motion of the first vertebra relative tothe second vertebra, and/or share a portion of the load applied to thevertebrae.

The dynamic posterior stabilization systems disclosed herein may allowfor rotational and/or translational motion of an elongated member (e.g.,a rod or plate) relative to one or more bone fasteners. The bonefasteners may include threading, barbs, rings or other protrusions thatsecure the bone fasteners to vertebrae. In some embodiments, the bonefasteners may be cemented or glued to the vertebrae. Bone fasteners mayinclude collars. In some embodiments, a collar of a bone fastener is anintegral portion of the bone fastener. In some embodiments, the collaris a separate component that is coupled to at least one other componentof the bone fastener. The collar of the bone fastener is the portion ofthe bone fastener that couples to an elongated member of the dynamicposterior stabilization system. In some embodiments, the bone fastenersare polyaxial pedicle screws and the collars are the upper portions ofthe polyaxial pedicle screws. In some embodiments, the bone fastenersare bone screws and the collars are plates, rod holders, or otherstructures that are coupled to the bone screws.

During installation of dynamic interbody devices of a spinalstabilization system, or during installation of a single dynamicinterbody device, one or both facet joints of the vertebrae may beremoved. A dynamic posterior stabilization system may be installed toreplace a removed facet joint. One or both of the dynamic interbodydevices of the spinal stabilization system, or the single dynamicinterbody device, may be coupled to a dynamic posterior stabilizationsystem. Coupling a dynamic interbody device to the dynamic posteriorstabilization system may inhibit backout of the dynamic interbody devicefrom the disc space.

In some embodiments, a dynamic posterior stabilization system may beinstalled without removal of a facet joint. The dynamic posteriorstabilization system may be installed after a discectomy, laminectomy,or other procedure. The dynamic posterior stabilization system maychange the dynamic resistance that is not normal due to degeneration,disease, loss of a portion of the intervertebral disc and/or tissuedamage.

A dynamic interbody device and a dynamic posterior stabilization systemmay include one or more biocompatible metals having a non-porous qualityand a smooth finish (e.g., surgical grade stainless steel, titaniumand/or titanium alloys). In some embodiments, a dynamic interbody deviceor dynamic posterior stabilization system may include ceramic and/or oneor more other suitable biocompatible materials, such as biocompatiblepolymers and/or biocompatible metals. Biocompatible polymers mayinclude, but are not limited to, polyetheretherketone resins (“PEEK”),carbon reinforced PEEK, ultra high molecular weight polyethylenes,polyethylenes, polyanhydrides, and alpha polyesters. For example, adynamic interbody device or a dynamic posterior stabilization system maybe constructed of a combination of biocompatible materials includingcobalt chromium molybdenum alloy, ultra high molecular weightpolyethylene, and polycarbonate—urethane or silicone blend.

Dynamic interbody devices may include surfaces that mate withcomplementary surfaces and allow for motion of vertebrae coupled to thedynamic interbody devices. Components or members of dynamic interbodydevices may be formed using CNC (computer numerical control) machiningor other techniques. Some surfaces of the dynamic interbody devices maybe treated to promote movement of the surfaces and/or to inhibitgalling. For example, two surfaces that move relative to each other mayhave mismatched hardness and/or different surface finish orientations topromote free movement of the surfaces relative to each other.

In some embodiments, dynamic interbody devices and dynamic posteriorstabilization systems may be made of non-magnetic, radiolucent materialsto allow unrestricted intra-operative and post-operative imaging.Certain material may interfere with x-ray and/or magnetic imaging.Magnetic materials may interfere with magnetic imaging techniques. Mostnon-magnetic stainless steels and cobalt chrome contain enough ironand/or nickel so that both magnetic imaging and x-ray imaging techniquesare adversely affected. Other materials, such as titanium and sometitanium alloys, are substantially iron free. Such materials may be usedwhen magnetic imaging techniques are to be used, but such materials areoften radio-opaque and sub-optimal for x-ray imagining techniques. Manyceramics and polymers are radiolucent and may be used with both magneticimaging techniques and x-ray imaging techniques. The dynamic interbodydevices and/or the dynamic posterior stabilization systems may includecoatings and/or markers that indicate the positions of the devicesand/or systems during operative and/or post-operative imaging.

In some embodiments, two dynamic interbody devices may be positioned ina disc space between two vertebrae during a spinal stabilizationprocedure. The largest width of each dynamic interbody device may beless than one half the width of the vertebrae the dynamic interbodydevices are to be positioned between. FIG. 1 depicts embodiments ofdynamic interbody devices 100′, 100″ that may be implanted using aposterior approach. Anterior ends and/or posterior ends of dynamicinterbody devices 100′, 100″ may be positioned near the edge of theendplates of vertebrae 102, 104 so that the dynamic interbody devicesabut strong, supportive bone of the vertebrae to be stabilized. Dynamicinterbody devices 100′, 100″ may be bilateral devices with coupled axialrotation and lateral bending.

FIG. 2 depicts a rear view of dynamic interbody devices 100′, 100″. Eachdynamic interbody device 100′ or 100″ may include first member 106,second member 108 and third member 110. First members 106 may be coupledto second members 108 so that dynamic interbody devices 100′, 100″accommodate lateral bending and axial rotation of vertebrae coupled tothe dynamic interbody devices. In some embodiments, dynamic interbodydevices 100′, 100″ couple lateral bending and axial motion together sothat lateral bending motion causes axial rotation, and axial rotationcauses lateral bending. Third members 110 may be coupled to secondmembers 108 so that dynamic interbody device 100′, 100″ accommodateflexion and extension of vertebrae coupled to the dynamic interbodydevice. Dynamic interbody devices 100′, 100″ are shown in positions ofneutral lateral bending, neutral axial rotation and maximum flexion inFIG. 2.

In some embodiments, the first members are coupled to the second membersto allow for lateral bending without coupled axial rotation. In someembodiments, the first members are coupled to the second members toallow for axial rotation without coupled lateral bending.

In some embodiments, first member 106 of dynamic interbody device 100′may be substantially a mirror image first member 106 of dynamicinterbody device 100″, and third member 110 of dynamic interbody device100′ may be substantially a mirror image of third member 110 of dynamicinterbody device 100″. In other embodiments, the first member of dynamicinterbody device 100′ may have a shape that is different than the mirrorimage of the first member of dynamic interbody device 100″ and/or thethird member of dynamic interbody device 100′ may have a shape that isdifferent than the mirror image of the third member of dynamic interbodydevice 100″.

Second member 108 of dynamic interbody device 100′ may be substantiallythe mirror image of second member 108 of dynamic interbody device 100″with the exception of second member 108 of dynamic interbody device 100′having portion 112 that engages portion 114 of second member 108 ofdynamic interbody device 100″ to join dynamic interbody device 100′ todynamic interbody device 100″ when the dynamic interbody devices arepositioned between vertebrae. In other embodiments, first member 106 ofdynamic interbody device 100′ has a portion that engages a portion offirst member 106 of dynamic interbody device 100″ when the dynamicinterbody devices are positioned between vertebrae. In otherembodiments, third member 110 of dynamic interbody device 100′ has aportion that engages a portion of first member 110 of dynamic interbodydevice 100″ when the dynamic interbody devices are positioned betweenvertebrae.

FIG. 3 depicts a front view of first member 106 of dynamic interbodydevice 100′. FIG. 4 depicts a side view of first member 106 of dynamicinterbody device 100′. FIG. 5 depicts a top view of first member 106 ofdynamic interbody device 100′. First member 106 may include keel 116,superior surface 118, slot 120, and opening 122. Keel 116 may reside ina groove or recess formed in a vertebra when dynamic interbody device100′ is positioned in a disc space between vertebrae. Keel 116 mayinhibit undesired movement of dynamic interbody device 100′ relative tothe vertebrae.

Superior surface 118 of first member 106 may be curved. The curvature ofsuperior surface 118 may complement a curvature of an inferior surfaceof the second member of the dynamic interbody device to allow thedynamic interbody device to accommodate lateral bending.

First member 106 may include arcuate slot 120. Arcuate slot 120 mayinteract with a complementary protrusion of the second member to allowthe dynamic interbody device to accommodate axial rotation. Thecurvature of superior surface 118 and arcuate slot 120 allows thedynamic interbody device to provide coupled lateral bending and axialrotation to vertebrae adjacent to the dynamic interbody device. In someembodiments, the second member may have an arcuate slot and the firstmember may have a complementary protrusion.

Arcuate slot 120 and the protrusion of the second member may bedovetailed or include another type of interconnection system thatinhibits non-rotational separation of first member 106 from the secondmember when the protrusion of the second member is engaged in the slotof the first member. End surfaces 124 of arcuate slot 120 may interactwith the end surfaces of the protrusion of the second member to resistshear load applied to the dynamic interbody device when the dynamicinterbody device is positioned between vertebrae. End surfaces 124 andthe end surfaces of the protrusion of the second member may be guidesfor lateral bending axial rotation of vertebrae coupled to the dynamicinterbody device.

First member 106 may include opening 122 in slot 120. A pin may bepositioned in opening 122. The pin may reside in a groove in the secondmember to define the maximum amount of lateral bending/axial rotationallowed by the dynamic interbody device. In other embodiments, a pinpositioned in an opening in the second member may reside in a groove inthe first member to define the maximum amount of lateral bending/axialrotation allowed by the dynamic interbody device.

FIG. 6 depicts a front view of second member 108 of dynamic interbodydevice 100′. FIG. 7 depicts a side view of second member 108 of dynamicinterbody device 100′. FIG. 8 depicts a top view of second member 108 ofdynamic interbody device 100′. FIG. 9 depicts a bottom view of secondmember 108 of dynamic interbody device 100′. Second member 108 mayinclude inferior surface 126, recessed surface 128, superior surface130, protrusion 132, bearing 134, tabs 136, groove 138, and portion 112.Some of inferior surface 126 may rest on the superior surface of thefirst member when protrusion 132 is placed in the arcuate slot of thefirst member. Inferior surface 126 may include a curvature thatcomplements the curvature of the superior surface of the first memberand protrusion 132 may complement the arcuate slot in the first memberso that the dynamic interbody device is able to accommodate coupledlateral bending and axial rotation of vertebra joined to the dynamicinterbody device

Portion 112 of second member 108 of the dynamic interbody device (shownin FIG. 6) may engage a complementary portion of the second member of asecond dynamic interbody device positioned adjacent to the dynamicinterbody device when the dynamic interbody devices are positioned in adisc space between vertebrae. FIG. 10 depicts second member 108 withportion 114 that complements portion 112 of second member shown in FIG.6. Engaging portion 112 with complementary portion 114 of the seconddynamic interbody device may stabilize the dynamic interbody deviceswhen the dynamic interbody devices are positioned between vertebrae.Coupling the dynamic interbody devices together with portions 112, 114may assure that the second members of the dynamic interbody devices movein tandem relative to the first members of the dynamic interbodydevices.

Coupling the dynamic interbody devices together with portions 112, 114may inhibit migration of the dynamic interbody devices and/or subsidenceof the vertebrae coupled to the dynamic interbody devices. Havingcomplementary portions may require that a specific dynamic interbodydevice be installed prior to the other dynamic interbody device duringan insertion procedure. For example, the dynamic interbody device with afemale connection portion (i.e., portion 114 in FIG. 10) may need to beinstalled first. After insertion, migration and/or removal of thedynamic interbody devices is only possible by reversing the insertionorder with the two dynamic interbody devices held in the same positionas during insertion (i.e., neutral in axial rotation and lateral bendingwhile in full flexion). Proper positioning of the two dynamic interbodydevices may be determined by examining the position of the connectedportions using imaging techniques before removal of the insertioninstruments.

As shown in FIG. 7, second member 108 may include bearing 134. Bearing134 may fit in a recess of the third member to allow the dynamicinterbody device to accommodate flexion and extension of vertebracoupled to the dynamic interbody device. Bearing 134 may include tabs136. Tabs 136 may fit in tracks in the third member to inhibitseparation of second member 108 from the third member. To assemble thedynamic interbody device, the third member may be coupled to the secondmember. The second member may be coupled to the first member. The firstmember will inhibit separation of the third member from the secondmember even when the dynamic interbody device is subjected to themaximum amount of extension.

As shown in FIG. 9, groove 138 may be formed in protrusion 132 of secondmember 108. In some embodiments, groove 138 may be open at one side ofsecond member 108. A pin in the first member may reside in groove 138 ofthe assembled dynamic interbody device.

Second member 108 may include recessed surface 128 in inferior surface126. Recessed surface 128 may allow a portion of second member 108 toextend over a portion of the first member of the second dynamicinterbody device without interference during lateral bending.

FIG. 11 depicts a perspective view that emphasizes bottom surface ofthird member 110. Third member 110 may include recess 140 with tracks142. Recess 140 and tracks 142 may complement the bearing and tabs ofthe second member.

As shown in FIG. 2, first member 106 of each dynamic interbody device100′, 100″ may include opening 144. Opening 144 may be a threadedopening or have another type of releasable coupling mechanism. Opening144 may be used to releasably couple the dynamic interbody device to aninsertion instrument. In other embodiments, openings for the insertioninstrument may be located in the second member and/or the third member.

The dynamic interbody device may include one or more features that allowthe insertion instrument to hold the dynamic interbody device in adesired position. For example, first member 106 may include slot 146 andthird member 110 may include slot 148. A portion of the insertioninstrument may be placed in slots 146, 148. The portion of the insertioninstrument that fits in slots 146, 148 may place the dynamic interbodydevice in a desired position for insertion between vertebrae (i.e.,neutral axial rotation, neutral lateral bending, and full flexion).

FIG. 12 depicts alternate embodiments of dynamic interbody devices 100′,100″ positioned between vertebra 102, 104. Each dynamic interbody devicemay include first member 106, second member 108 and third member 110.First member 106 and second member 108 may include complementary curvedridges that allow for coupled lateral bending and axial rotation ofvertebrae 102, 104 that the dynamic interbody devices are positionedbetween. In some embodiments, the second member includes a guide recess.A guide pin of the first member resides in the guide recess to join thefirst member and the second member together and/or to limit the amountof axial rotation and lateral bending allowed by the dynamic interbodydevice. The first member may include undercut surfaces. The undercutsurfaces of the first member may interact with undercut surfaces of thesecond member to inhibit separation of the first member from the secondmember and to take a portion of the shear load applied to the dynamicinterbody device.

A tab of third member 110 may be placed in a slot of second member 108.A pin may be positioned in second member 108 through an opening in theslot to join the second member to third member 110. Second member 108may include bearing 134. Third member 110 may include a recess with acurved surface that complements the curve of bearing 134. The couplingof the recess of third member 110 with the bearing of second member 108may accommodate flexion and extension of vertebrae 102, 104 that dynamicinterbody devices 100′, 100″ are positioned between.

Dynamic interbody devices 100′, 100″ work in conjunction to allow forcoupled lateral bending and axial rotation and/or flexion/extension ofvertebrae 102, 104 the dynamic interbody devices are positioned between.During an insertion procedure, careful positioning of the dynamicinterbody devices 100′, 100″ may be needed to ensure that dynamicinterbody device 100′ works in conjunction with dynamic interbody device100″. In some dynamic interbody device embodiments, a separation angleof about 30° (i.e., each implant oriented at about 15° from a centerline of endplate of the lower vertebra being stabilized) is desiredbetween dynamic interbody devices 100′, 100″. In some dynamic interbodydevice embodiments, a separation angle of about 24° (i.e., each implantoriented at about 12° from a center line of endplate of the lowervertebra being stabilized) is desired between dynamic interbody devices100′, 100″. Other embodiments of dynamic interbody devices may bedesigned to operate in conjunction with each other at other separationangles.

In some embodiments, insertion instruments may allow insertion ofdynamic interbody devices 100′, 100″ so that ends of the dynamicinterbody devices touch. Intra-operative imaging may be used to ensurethe proper positioning and alignment of the dynamic interbody devices.In some embodiments, a portion of dynamic interbody device 100′ mayengage a portion of dynamic interbody device 100″ to ensure properpositioning of the dynamic interbody devices 100′, 100″. For example, adovetailed portion of dynamic interbody device 100′ fits in acomplementary groove of dynamic interbody device 100″ when the dynamicinterbody devices are properly positioned. Engaging dynamic interbodydevices may inhibit migration of the dynamic interbody devices afterinsertion.

FIG. 13 depicts the posterior end of dynamic interbody device 100′ whenthere is no lateral bending or axial rotation of second member 108 ofthe dynamic interbody device relative to first member 106. In someembodiments, first member 106 may be wider than second member 108 andthird member 110. First member 106 may abut the lower vertebra of thevertebrae to be stabilized. Having the first member wider than secondmember 108 and/or third member 110 may take advantage of the spaceavailable for insertion of the dynamic interbody devices between thevertebrae.

In many previous devices inserted using a posterior approach, the widthof the portion of the device that contacted the upper vertebra wassubstantially the same as the width of the portion of the device thatcontacted the lower vertebra. The width of devices was typically thelargest width that allowed insertion of the portion of the device thatcontacted the upper vertebra without undue retraction of neuralstructures exiting between the vertebrae. The space available forinsertion of a device using a posterior approach is typically wider nearthe lower vertebra and becomes less wide nearer the upper vertebra.

In some embodiments, second member 108 and third member 110 may includecurved dovetailed slots 150. Slots 150 may accept a first portion of aninserter. When the first portion of the inserter is coupled to slots 150of second member 108 and third member 110, movement of the second memberrelative to the third member (e.g., flexion/extension) is inhibited.First member 106 may include inserter opening 144. Inserter opening 144may be threaded. A second portion of the inserter may fit in inserteropening 144. When the first portion of the inserter is coupled to slots150 and the second portion of the inserter is positioned in inserteropening 144, movement of first member 106 relative to second member 108is inhibited.

The first member of the dynamic interbody device may be wider than thethird member to take advantage of the available insertion space for thedynamic interbody devices. Having first members with large widthsprovides large contact area between the first members and the lowervertebra. The large contact area may inhibit subsidence of the vertebrathat is more likely to subside due to the presence of the dynamicinterbody devices. Even though third member may be less wide than firstmember, the third member provides sufficient contact against the uppervertebra to inhibit subsidence of the upper vertebra.

Pairs of dynamic interbody devices having different widths, lengths,and/or heights may be provided in the instrument kit for the spinalstabilization procedure. For example, the instrument kit may includepairs of implants having small widths, medium widths, and large widthsof different heights and/or lengths.

In some embodiments, a dynamic interbody device or dynamic interbodydevices may not allow coupled axial rotation and lateral bending ofvertebrae adjacent to the dynamic interbody device or dynamic interbodydevices. For example, in an embodiment, the curvature of ridges in thefirst member and second member of the dynamic interbody device onlyallows for axial rotation of vertebrae adjacent to the dynamic interbodydevice without allowing for lateral bending. The interaction of thefirst member with the second member allows for axial rotation andresists at least a portion of the shear load applied by the vertebrae tothe dynamic interbody device. In an embodiment, the curvature of ridgesin the first member and the second member allow for lateral bending ofvertebrae adjacent to the dynamic interbody device without allowing foraxial rotation. The interaction of the first member with the secondmember allows for lateral bending and resists at least a portion of theshear load applied by the vertebrae to the dynamic interbody device.

FIG. 14 depicts a perspective view of embodiments of dynamic interbodydevices 100′, 100″. Each dynamic interbody device 100′, 100″ may includefirst member 106, second member 108 and third member 110. First member106 may include inserter opening 144. Inserter opening 144 may bethreaded. First member 106 and third member 110 may also includeopenings 152. Ends of an insertion instrument may be positioned inopenings 152 to fix the position of first member 106 relative to thirdmember 110 during insertion.

An instrument kit for a surgical procedure may include a number dynamicinterbody devices 100′, 100″ having different heights. In someembodiments, the position of inserter opening 144 and/or openings 152 isdifferent for dynamic interbody devices 100′, 100″ with differentheights so that only the appropriate insertion instruments can be usedwith the dynamic interbody devices. In some embodiments, the position ofinserter opening 144 and openings 152 is the same for all dynamicinterbody devices so that only two insertion instruments are needed forthe instrument kit (an insertion instrument for dynamic interbody device100′ and an insertion instrument for dynamic interbody device 100″).

FIG. 15 depicts a bottom view of dynamic interbody devices 100′, 100″.Dynamic interbody devices 100′, 100″ may include pins 154, keels 116,and recessed areas 156. Each pin 154 may couple first member 106 to thesecond member of the dynamic interbody device. Keels 116 may securedynamic interbody devices 100′, 100″ to the vertebra. During thesurgical procedure to install dynamic interbody devices 100′, 100″, aframework may be formed for positioning sizing tools and insertioninstruments that allow properly sized dynamic interbody devices to bepositioned at desired locations. Portions of the framework may includeguides that allow a drill bit to form openings in the vertebra for keels116.

Recessed areas 156 may have a depth of about 0.35 mm. Other depths maybe used. A porous titanium coating or other material that promotesimplant retention may be formed or placed in recessed area 156. Bone ofthe vertebra that first member 106 is placed against may bond to theporous titanium coating. Initially, the rough surface of the poroustitanium coating may provide resistance to migration of the dynamicinterbody device until rigid fixation is achieved when the bone bonds tothe porous titanium coating.

FIG. 16 depicts a side view of first member 106 of dynamic interbodydevice 100′ depicted in FIG. 14. First member 106 may include keel 116,curved ridge 158, curved groove 160, superior surface 118, andprotrusion 162. Keel 116 may include neck 164 and base 166. Base 166 maybe a cylinder that is wider than neck 164. The width of base 166 ascompared to neck 164 inhibits keel 116 from lifting out of the vertebra.Neck 164 and base 166 may have angled portions at the anterior ends. Theangled portions may facilitate insertion into the vertebra.

Curved ridge 158 may be positioned in a groove in the second member ofthe dynamic interbody device. An engaging portion of the second membermay be placed in curved groove 160. Angled surface 168 and thecorresponding angled surface of the engaging portion of the secondmember inhibit vertical separation of first member 106 from the secondmember. After the second member is coupled to first member 106, a pinmay be positioned in opening 122 in groove 160 to secure the firstmember to the second member. The pin may provide a limit to the amountof axial rotation and/or lateral bending of vertebrae coupled to thedynamic interbody device allowed by the dynamic interbody device.

During the surgical procedure to install the dynamic interbody devicesin a disc space formed between two vertebrae, protrusion 162 may beplaced in an opening in an end portion of the other dynamic interbodydevice (end portion 170 depicted in FIG. 15). The framework formedduring the insertion procedure may facilitate placement of the dynamicinterbody devices so that protrusion 162 is positionable in the openingin the end portion of the other dynamic interbody device. Protrusion 162may have a tapered bullet shape to facilitate placement of theprotrusion in the opening in the end portion of the other dynamicinterbody device. Images may be taken during the installation procedureto ensure that the dynamic interbody devices are properly positionedrelative to each other.

FIG. 17 and FIG. 18 depict perspective views of second member 108 ofdynamic interbody device 100″ depicted in FIG. 14. Second member 108 mayinclude angled groove 172, engaging portion 174, curved surface 176, andbearing 134. The ridge of the first member may fit in angled groove 172of second member 108. Movement of second member 108 relative to ridgeallowed by angled groove 172 may allow the dynamic interbody device toaccommodate axial rotation of vertebrae coupled to the dynamic interbodydevice. Angled groove 172 may also include slot 178. Slot 178 may acceptan end of a pin or other projection that is positioned in the firstmember during assembly of the dynamic interbody device. Positioning thepin in slot 178 inhibits separation of the first member from secondmember 108 and provides a limit to the range of motion of axial rotationand lateral bending allowed by the dynamic interbody device.

Engaging portion 174 may fit in the groove of the first member. Angledsurface 180 of engaging portion may complement the angled surface of thegroove in the first member. The angled surfaces may interact to inhibitvertical separation of the first member from second member 108.

Curved surface 176 of second member 108 may complement the superiorsurface of the first member. The complementary surfaces may allow thedynamic interbody device to accommodate lateral bending of vertebraecoupled to the dynamic interbody device.

Bearing 134 may be positioned in a recess in the third member. Bearing134 may allow the dynamic interbody device to accommodate flexion andextension of vertebra coupled to the dynamic interbody device. Secondmember 108 may include channel 182 on each side of bearing 134. Channel182 may include an entry portion and a curved portion. A ball bearingmay be positioned in each channel 182 during assembly of the dynamicinterbody device. The ball bearings allow the third member to move inflexion and extension relative to second member 108 and inhibitseparation of the third member from the second member.

FIG. 19 depicts a perspective view of third member 110 that emphasizesthe bottom surface of the third member. Third member 110 may includerecess 184 defined by arms 186. Recess 184 may complement the bearing ofthe second member. Opening 188 may be formed in each arm 186. A ballbearing may be positioned in each opening 188 during assembly of thedynamic interbody device.

FIG. 20 depicts a perspective view of third member 110 that emphasizesthe top surface of the third member. Openings 188 extend from the topsurface to the recess on the bottom side of third member 110. Thirdmember 110 may include recessed area 190. Recessed areas 190 may have adepth of about 0.35 mm. Other depths may be used. A porous titaniumcoating or other material that promotes implant retention may be formedor placed in recessed area 190. Bone of the vertebra that third member110 is placed against may bond to the porous titanium coating.Initially, the rough surface of the porous titanium coating may provideresistance to migration of the dynamic interbody device until rigidfixation is achieved when the bone bonds to the porous titanium coating.

During assembly of the dynamic interbody device, the bearing of thesecond member may be placed in the recess of the third member. The thirdmember may be tilted relative to the second member so that the openingsin the arms of the third member align with the entry portions of thechannels in the bearings in the second members. A ball bearing may beplaced in each opening. The ball bearings may fall adjacent to thebeginning of the arced portions of the channels in the second member.The third member may be tilted downwards towards the engaging portion ofthe second member so that the entry portions of the groove are notaligned with the openings in the third member to trap the ball bearingsin the arced portions of the channels.

The engaging portion of the second member may be positioned at thegroove in the first member. The second member/third member combinationmay be pushed into the first member so that the curved ridge of thefirst member is positioned in the groove of the second member and theengaging portion of the second member is positioned in the curved grooveof the first member. A pin may be press fit into the opening in thefirst member so that the end of the pin resides in the slot in thesecond member. When the third member is rotated, the bottom posteriorsurface of the third member contacts the upper posterior surface of thefirst member before the opening in the third member aligns with theupper portion of the channel in the second member, thus preventing thepossibility of removal of the ball bearings from the dynamic interbodydevice.

In some embodiments, the third members of the dynamic interbody devicesare domed. For example, the upper surfaces of the third members have adome approximately 1 mm in height to better conform to the concavesurface of the upper vertebra. The domed surface may provide immediateand long-term retention of the dynamic interbody devices in the discspace.

For some dynamic interbody devices, the vertebra contact surface of thefirst member is larger than the vertebral contact surface of the thirdmember. The larger vertebral contact surface of the first member mimicsthe anatomy of the surgical canal. Table 1 gives values for four dynamicinterbody device sizes. The AP Length is the anterior-posterior length.The Lower Width is the width across the lower surface of the firstmember. The T Width is the transverse width of a pair of assembleddynamic interbody device measured from the lower surface of the firstmember of each dynamic interbody device (i.e., width T depicted in FIG.15). Upper Area is the footprint area of the contact surface of thethird member. Lower Area is the footprint area of the contact surface ofthe first member, not excluding the keel.

TABLE 1 AP Lower T Upper Lower Length Width Width Area Area Size (mm)(mm) (mm) (mm²) (mm²) 1 24 13 31.3 557 557 2 26.7 13.7 33.9 633 679 329.3 14.5 36.5 706 797 4 32 15 38.6 777 906

The above noted sizes were chosen based on a statistical sizing analysisof percentile groupings of male and female vertebral body endplates. ForL4-L5 and L5-S1 male and female vertebral bodies, the estimatedvertebral body endplate coverage of ideally sized and placed dynamicinterbody devices ranged from 38% (95^(th) percentile L4-L5 upperendplate for males) to 63% (5^(th) percentile L5-S1 lower endplate forfemales) with an overall average endplate coverage of 53%. A 30% to 40%coverage may be sufficient to prevent subsidence into cancellous boneunder physiologic axial loads. Portions of the dynamic interbody devicesare positioned on the endplates of the vertebral bodies near thepedicles. These regions are high strength regions of the vertebralbodies that provide extra subsidence residence as compared to interbodydevices that are designed to be centrally positioned on the endplates.

In some embodiments, a single dynamic interbody device may be used. FIG.21 depicts a perspective view of dynamic interbody device 100emphasizing the anterior side and the superior surface. Dynamicinterbody device 100 is shown with some axial rotation and lateralbending from a neutral position. Dynamic interbody device 100 may beplaced in a disc space between two vertebrae using an anterior approach.The width of the dynamic interbody device may be greater that one halfthe width of the vertebrae the dynamic interbody device is to bepositioned between. The width of the dynamic interbody device may besubstantially the same as the width of the vertebrae the dynamicinterbody device is to be positioned between. Dynamic interbody device100 may include first member 106, second member 108, and third member110. Dynamic interbody device 100 may be a bilateral device with coupledaxial rotation and lateral bending. First member 106 may be coupled tosecond member 108 so that dynamic interbody device 100 accommodateslateral bending and axial rotation of vertebrae coupled to dynamicinterbody device 100. As with a natural functional spinal unit, dynamicinterbody device 100 couples lateral bending and axial motion togetherso that lateral bending motion causes axial rotation, and axial rotationcauses lateral bending. Third member 110 may be coupled to second member108 so that dynamic interbody device 100 accommodates flexion andextension of vertebrae coupled to the dynamic interbody device.

The superior surface may be coupled to an upper vertebra of thevertebrae to be stabilized. An inferior surface of the dynamic interbodydevice may be coupled to the lower vertebra of the vertebrae to bestabilized. At least a portion the superior surface may be positionednear the edge of the endplate of the upper vertebra so that the dynamicinterbody device abuts strong, supportive bone of the upper vertebra. Atleast a portion of the inferior surface may be positioned near the edgeof the endplate of the lower vertebra so that the dynamic interbodydevice abuts strong, supportive bone of the lower vertebra.

FIG. 22 depicts a side view of first member 106 and FIG. 23 depicts atop view of the first member. First member 106 may include ridges 192and pin opening 194. Ridges 192 and the grooves between the ridges maymate with corresponding grooves and ridges of the second member so thatthe dynamic interbody device accommodates coupled lateral bending andaxial rotation. As depicted in FIG. 23, ridges 192 may be curved. Thecurvature allows the dynamic interbody device to accommodate axialrotation. Ridges 192 may be symmetrical about center line 196 of firstmember 106 so that the dynamic interbody device accommodates the sameamount of clockwise axial rotation as counterclockwise axial rotation.In some embodiments, the ridges and grooves may not be symmetrical aboutthe centerline so that the dynamic interbody device allows no or limitedaxial rotation in a particular direction to accommodate the needs of apatient.

A guide pin may be press fit or otherwise secured in pin opening 194after the second member is coupled to first member 106. The guide pinmay fit in a guide recess in the second member. The guide pin may limitthe amount of lateral bending and axial rotation allowed by the dynamicinterbody device and/or inhibit separation of first member 106 from thesecond member. In some embodiments, the first member may have a guiderecess and a guide pin may positioned in the second member may reside inthe guide recess.

As seen in FIG. 22, first member 106 may include one or more undercutsurfaces 198. Undercut surfaces 198 may inhibit separation of the secondmember from first member 106 when the second member is coupled to thefirst member. Undercut surfaces 198 may share a portion of the loadapplied to the dynamic interbody device.

FIG. 24 depicts a front view of first member 106. First member 106 maydecrease in height from a position at or near the right side of thefirst member to the center of the first member. The first member 106 mayincrease in height from the center to a position near or at the leftside of the first member. At least a portion of first member 106 has aconcave shape. The concave shape of at least a portion of first member106 may allow the dynamic interbody device to accommodate lateralbending of vertebrae coupled to the dynamic interbody device.

FIG. 25 depicts a side view of second member 108. The bottom of secondmember 108 may include ridges 200, one or more undercut surfaces 202,and guide recess 204. Ridges 200 may be curved and the bottom of secondmember 108 may have a convex shape so that the ridges of the secondmember mate with the grooves between the ridges of the first member, andthe ridges of the first member mate with the grooves between the ridgesof the second member. Undercut surfaces 202 may interact with theundercut surfaces of the first member to inhibit separation of secondmember 108 from the first member when the dynamic interbody device isassembled. An end of the guide pin placed in the pin opening of thefirst member may reside in guide recess 204 of second member. The guidepin may limit the range of motion for axial rotation and lateral bendingof the assembled dynamic interbody device and inhibit separation of thefirst member from second member 108.

Second member 108 may include bearing 134. Bearing 134 may fit in arecess in the third member so that the assembled dynamic interbodydevice is able to accommodate flexion and/or extension of vertebraecoupled to the dynamic interbody device. Other connection systemsbetween the second member and the third member that accommodateflexion/extension of vertebrae coupled to the dynamic interbody devicemay also be used.

In some embodiments, the second member includes a bearing recess and thethird member includes a bearing that fits in the recess. Bearing 134 maybe located towards a posterior end of the dynamic interbody device.Locating bearing 134 near the posterior end of the dynamic interbodydevice locates the axis of rotation for flexion/extension close to thenatural axis of rotation for flexion/extension of the vertebrae. Thecurvature of bearing 134 may be relative small to limit translationalmovement of the third member relative to second member duringflexion/extension.

FIG. 26 depicts a top surface of second member 108. Second member 108may include slots 206. Tabs of the third member may be positioned inslots 206. One or more pins positioned in bearing 134 of second member108 and through the tabs of the third member may couple the secondmember to the third member. When the dynamic interbody device ispositioned between vertebrae, fluid may enter the slots and keep thedynamic interbody device lubricated.

In some embodiments, the second member of the dynamic interbody devicemay have a protrusion and the first member may have a complementary slotinstead of a plurality of complementary ridges and grooves. In someembodiments, the second member of the dynamic interbody device may havea slot and the first member may have a complementary protrusion insteadof a plurality of complementary ridges and grooves in the second memberand the first member.

FIG. 27 depicts a perspective view of third member 110 that emphasizes abottom surface of the third member. Third member 110 may include recess208 and tabs 210. Recess 208 may be complementary to the bearing of thesecond member so that the assembled dynamic interbody device allows forflexion/extension of vertebrae coupled to the dynamic interbody device.Tabs 210 may be positioned in the slots of the second member. A pin orpins positioned through openings 212 in tabs 210 may couple third member110 to the second member.

In some embodiments, the front faces of the first member, second memberand/or third member may include indentions, openings, or other surfacefeatures for connecting the dynamic interbody device to an inserter. Theconnection between the dynamic interbody device and the inserter allowsforce to be applied substantially evenly to the dynamic interbody deviceto facilitate insertion of the dynamic interbody device into the discspace. The inserter may maintain the position of the first memberrelative to the second member and the third member during insertion.

The ridges of the first member are complementary to the ridges of thesecond member. When the dynamic interbody device is positioned betweenvertebrae, the vertebrae exert compressive and/or shear forces on thedynamic interbody device. Having a number of ridges increases thesurface area for dissipating force applied to the dynamic interbodydevice. Increasing the surface area for dissipating force applied to thedynamic interbody device may reduce pressure and decrease wear of thedynamic interbody device.

A front part of the third member may rotate towards the second member toaccommodate flexion. The front part of the third member may rotate awayfrom the second member to accommodate extension.

Dynamic posterior stabilization systems may be used to support vertebraeand/or to provide resistance to motion of a first vertebra relative to asecond vertebra. FIG. 28 depicts an embodiment of in-line dynamicposterior stabilization system 214. Dynamic posterior stabilizationsystem 214 may include first bone fastener 216, second bone fastener218, and dampener system 220. An instrument kit supplied for a spinalstabilization procedure may include a number of bone fasteners anddampener systems that allow for the formation of dynamic posteriorstabilization systems.

An elongated member of dampener system 220 is positioned directlybetween collars of first bone fastener 216 and second bone fastener 218in an in-line system. In some embodiments, the dampener system may beoffset from both of the bone fasteners to accommodate space restrictionsin the patient. In some embodiments, the dynamic posterior stabilizationsystem includes an offset member that couples to the second bonefastener to allow the dampener system to be positioned to one side ofthe second bone fastener. The offset member may allow the dampenersystem to be positioned towards the spine (medially) or away from thespine (laterally). Positioning the dampener system to one side of thesecond bone fastener allows a second dampener system of a multi-levelconstruct to be attached to the collar of the second bone fastener. Indynamic posterior stabilization systems where the dampener system isoffset from one of the bone fasteners, a transverse connector to adynamic posterior stabilization system on an opposite side of the spinemay be needed to counteract moments generated when force is applied tothe dynamic posterior stabilization system due to the offset position ofthe bone fastener relative to the dampener system.

The bone fasteners of dynamic posterior stabilization system 214 may bepedicle screws, clamps, hooks, barbs, or other fasteners that secure tovertebrae. In some embodiments, the bone fasteners are pedicle screws.The pedicle screws may include self-tapping thread. In some embodiments,the pedicle screws are polyaxial pedicle screws. In some embodiments,the bone fasteners are non-polyaxial pedicle screws.

FIG. 29 depicts an exploded view of an embodiment of first bone fastener216 that includes collar 222, threaded shaft 224 and closure member 226.Collar 222 may be press fit or otherwise secured to threaded shaft 224.An opening through a bottom portion of collar 222 allows an end of adriver to couple to a tool opening in threaded shaft 224 so that thethreaded shaft may be driven into a vertebra.

In some embodiments, a portion of threaded shaft 224 near collar 222 hasa porous titanium coating. The porous titanium coating may enhancefixation of the bone fastener to bone. Only having a portion of thethreaded shaft with the porous titanium coating may allow for removal ofthe bone fastener during a revision surgery. In some embodiments, theentire length of the threaded shaft may have a porous titanium coating.

Closure member 226 may be attached to collar 222 to secure a portion ofthe dampener system to the bone fastener. In some embodiments, closuremember 226 includes threading that engages threading in collar 222. Insome embodiments, the closure member may snap onto the collar. In someembodiments, a bottom portion of closure member 226 includes one or moreridges or projections that engage the portion of the dampener systempositioned in the collar to securely hold the dampener system in thecollar. The ridges or projections may bite into or deform against theportion of the dampener system positioned in the collar.

In some embodiments, an offset member of a dampener system may slideover collar 222. The offset member allows the dampener system to bepositioned medial or lateral to the bone fastener. The bottom of theoffset member may be positioned against base 228 of threaded shaft 224.When the bottom of the offset member is positioned against base 228 ofthreaded shaft 224, the top of the offset member may be substantiallyeven with the top of arms 230 of collar 222. Top portion 232 of closuremember 226 may extend past arms 230 of collar 222 to inhibit removal ofthe offset member when the closure member is coupled to the collar.

In some embodiments, the first bone fastener is identical to the secondbone fastener. In some embodiments, the first bone fastener may by adifferent type of fastener, and/or have a different collar, size, and/orlength than the second bone fastener. For example, FIG. 30 depicts anembodiment of second bone fastener 218 that is different than first bonefastener 216 depicted in FIG. 29. Arms 230 of second bone fastener 218depicted in FIG. 30 may snap onto a sleeve positioned in collar 222 ofthe second bone fastener to secure the sleeve to the second bonefastener. The use of snap-on arms may eliminate the need for a closuremember for the bone fastener.

In some embodiments, the first bone fastener is identical to the secondbone fastener. FIG. 31 depicts an embodiment of a bone fastener for anin-line dynamic posterior stabilization system that may be used as firstbone fastener 216 or second bone fastener 218. The bone fastener mayinclude collar 222, threaded shaft 224 and closure member 226. In someembodiments, collar 222 is about 15 mm high, about 11.6 mm wide, about 8mm thick. Collar 222 may have other dimensions.

Collar 222 may include slots 234 and ledges 236 on each side of thecollar. Arms 238 of closure member 226 may fit in slots 234. Grooves 240in arms 238 may snap over ledges 236 of collar 222 to secure closuremember 226 to the collar. Closure member 226 may include threadedopening 242. An insertion tool may be attached to threaded opening 242to facilitate attachment of closure member 226 to collar 222. Theinsertion tool may also be used to remove closure member 226 from collar222. A threaded end of the insertion tool may be attached to threadedopening 242. The insertion tool may be rotated to contact the end of theinsertion tool against an object positioned in collar (e.g., a ball orelongated member of a dampener system). Continued rotation of theinsertion tool will apply upward force to closure member 226 that pullsgrooves 240 past ledges 236 and allows closure member 226 to be removedfrom collar 222.

The inside surface of collar 222 may be a smooth spherical surface. Aball of a dampener system may be positioned in collar 222. The ball ofthe dampener system may articulate in collar 222. The articulation maybe unlimited in axial rotation. The articulation may have about ±13°range of motion in the medial-lateral direction and ±24° in theanterior-posterior direction. The limits of motion may occur when aportion of the dampener system (e.g., the elongated member) contacts theinside edges of collar 222.

Collar 222 may include concave recesses 244 on each side of the collar.Convex portions of washers of the dampener system may be positioned inconcave recesses 244. Concave recesses 244 may interact with the convexportions of the washers to center the dampener system in collar 222. Thedampener system may articulate within collar 222. The range of motion ofthe dampener system relative to the collar may be about ±10° in themedial-lateral direction, about ±23° in the anterior-posteriordirection, and about ±35° in axial rotation.

Dampener systems may be preassembled as single units. The dampenersystems may be included in an instrument kit for the spinalstabilization procedure. The instrument kit supplied for a surgicalprocedure may include a number of different bone fasteners. Bonefasteners may be provided in a variety of lengths and thread diameters.In some embodiments, the instrument kit includes bone fasteners withlengths ranging from about 30 to about 55 mm in 5 mm increments. Bonefasteners of a specific length may have the same color and/or includeindicia indicating the length. In some embodiments, the instrument kitincludes two sets of bone fasteners, each set having a different threaddiameter. For example, the first bone fastener set may have a threaddiameter of about 6.0 mm and the second set may have a thread diameterof 7.0 mm. The 6.0 mm thread diameter bone fasteners may be the standardbone fasteners used in most procedures. The 7.0 mm thread diameter bonefasteners may be used in the event of a revision surgery after removalof the smaller bone fastener. The bone fasteners may be color codedand/or include indicia that indicates the thread diameter of the bonefasteners.

The instrument kit may include dampener systems having various lengths.Lengths of dampener systems refer to the interpedicular distancemeasured between centers of collars of the bone fasteners. For a singlelevel spinal stabilization procedure for two adjacent vertebrae, theinstrument kit may include dampener systems ranging in length from about25 mm to about 35 mm in 5 mm increments. Other lengths and/or sizeincrements may be provided. Also, the length of the dampener systems maybe adjustable by ±2.5 mm by rotating a portion (e.g., a ball) of thedampener system. The dampener systems may be color coded and/or includeindicia that indicate the lengths of the dampener sets.

In some embodiments, the dampener systems are isolated dual dampenersystems. One dampener set provides resistance to flexion and anotherdampener set provides resistance to extension in dual dampener systems.In some embodiments, the dampener systems are partially shared dualdampener systems. One dampener set provides resistance to extension andboth dampener sets provide resistance to flexion in shared dual dampenersystems. In some embodiments, the dampener systems are single dampenersystems. One dampener set provides resistance to both flexion andextension in single dampener systems.

A dampener set may be a single dampener or a plurality of dampeners. Thedampeners may be elastic washers, elastic tubes, springs, or othersystems that provide resistance to compression. The dampener sets mayhave non-linear compression characteristics such that the dampener setsare initially easier to compress and then become stiffer. The use ofdampener sets with non-linear compression characteristics may allow fora large neutral zone (10-50% of the total range of motion) where thestiffness in the neutral zone is about 10-30% of the stiffness outsideof the neutral zone.

Dampener sets may be made of biocompatible material. The dampener setmaterial may be able to undergo large deformations for millions ofcycles. The dampener set material may be fatigue and wear resistantunder large deformations (e.g., ˜50% or more). In some embodiments, thedampener sets may be made of materials having non-linear compressionbehavior that approximates or matches the behavior of the normal spinein flexion/extension, and/or lateral bending. In some embodiments, thedampener sets may be made of material or materials having linearcompression behavior. The material shape and/or the configuration oflinear materials may allow for non-linear compression behavior thatapproximates or matches the behavior of the normal spine inflexion-extension and/or lateral bending.

The material used to form dampener sets may be elastic foam. Materialsthat may be used to form the dampener sets are silicone elastomers.Silicone elastomers may be available from NuSil Silicone Technology,LLC. (Carpinteria, Calif.). Other types of elastomers may also be used.FIG. 32 depicts stress-strain behavior required by dampener sets toallow for normal physiological motion of a reconstructed function spinalunit plotted along with measured compressive stress-strain curves forfour silicone elastomers. Data for curve 246 is based on in vitrotesting data from isolated lumbar functional spinal units. Data forcurve 248 is based on in vitro testing data from whole lumbar spines.The remaining curves depict stress strain behavior of siliconeelastomers available from NuSil Technology, LLC. Curve 250 depictsstress-strain for 80 durometer, unrestricted LSR (liquid siliconerubber) elastomer (MED-4880). Curves 252, 254, 256 depict curves forunrestricted high-consistency elastomers. Curve 252 corresponds to 70durometer MED-4770, curve 254 corresponds 55 durometer MED-4755, andcurve 256 corresponds to 50 durometer MED 4719. Line 260 depicts anapproximation of the maximum in vivo stress on a dampener set. Line 262depicts an approximation of the maximum in vivo strain on a dampenerset. The non-linearity of the elastomers match well with the estimatedrequirements for the dampener sets.

FIG. 33 depicts dampener set load when compressed after 0.5 million, 1million and 2 million compression cycles to 20% or 40% strain for 70durometer silicone elastomers. Curve 264 is for 20% fatigue strain for agamma sterilized material. Curve 266 is for 40% fatigue strain for agamma sterilized material. Curve 268 is for 40% fatigue strain for anunsterilized material. The load decreased slightly (up to approximately15%) following the first 0.5 million cycles and then remainedessentially constant for up to 2 million cycles. Gamma sterilizationresulted in a slight load loss for the material.

FIG. 34 depicts dampener set resting length after 0.5 million, 1 millionand 2 million compression cycles to 20% or 40% strain for 70 durometersilicone elastomers. Curve 270 is for 20% fatigue strain for a gammasterilized material. Curve 272 is for 40% fatigue strain for a gammasterilized material. Curve 274 is for 40% fatigue strain for anunsterilized material. The resting length of the dampener sets did notappreciably decrease after 2 million compression cycles. The amount ofpermanent length reduction was less than about 5% following repetitivecycling loading with strain below 50% of the initial dampener length.

A dampener set may be pre-compressed during assembly of the dampenersystem. For example, a length of a dampener set before assembly into adampener system may be about 15% longer than the length of the dampenerset after assembly into the dampener system. Pre-compressing thedampener set may accommodate any permanent deformation of the dampenerset due to repetitive loading. Pre-compressing the dampener set may alsoinhibit formation of a gap between the dampener set and other portionsof the dampener system when the dampener system is in a neutralposition.

In some embodiments, non-linear dampener set behavior may be obtainedusing materials that do not have inherent non-linear properties.Non-linear dampener behavior may be obtained by altering the dampenerset design from a simple cylinder design. For example, a first elastomerwith a first length may be positioned concentrically inside or outsideof a second elastomer with a length that is different from the firstlength. FIG. 35 depicts a cross-sectional representation of a portion ofa dampener system with dampener sets 276 of concentrically positionedelastomers. Inner dampener 278 may be made of a material having a firstmodulus of elasticity. Outer dampener 280 may be made of a materialhaving a lower modulus of elasticity. In some embodiments, the materialused to form the outer dampener is the same material as the materialused to form the inner dampener. In some embodiments, the material usedto form the inner dampener and/or the outer dampener has substantiallylinear compression behavior. In some embodiments, the material used toform the inner dampener and/or the outer dampener has non-linearcompression behavior.

Computer simulations may be used to model compression behavior ofmaterials. FIG. 36B depicts a plot of force versus displacement forsimulated compression of concentric dampener set 276 depicted in crosssection in FIG. 36A. FIG. 37B depicts a plot of force versusdisplacement for simulated compression of concentric dampener set 276depicted in cross section in FIG. 37A.

In some embodiments, non-linear dampener set behavior may be obtained bychanging the shape of the dampener set. FIG. 38 depicts a side viewrepresentation of dampener set 276 that is formed of a stack of smalldampeners 282. FIG. 39 depicts a perspective view of one dampener 282.Dampener 282 may be shaped so that the initial area of contact betweentwo dampeners is relatively small. When dampeners 282 are compressed,additional contact area between two dampeners develops.

In some embodiments, a modified single piece dampener set may be usedinstead of a stack of small dampeners. FIG. 40A depicts a cross sectionof an embodiment of dampener set 276 with alternating segments of largeand small diameter. Dampener set 276 may be molded as a single piece.FIG. 40B depicts a plot of force versus displacement for the simulatedcompression of the dampener set depicted in FIG. 40A.

Dampener sets may be subjected to significant fatigue and wearrequirements. Dampener set geometry and/or arrangement may be altered toincrease the operating life of the dampener set. A common location forcracks to form is the center of the inside diameter of the dampener set.As shown in FIG. 41, fillets 284 may be formed at other locations indampener set 276 to relieve the stress applied at the center of theinside diameter of dampener set 276. In other embodiments, the dampenerset may be formed of two or more segments so that the maximum stress islocated at two or more locations in the dampener set. FIG. 42 depictsdampener set 276 formed of a number of segments 286.

In some embodiments, dampener set may have a barrel shape. FIG. 43depicts dampener set 276 with a barrel shape. A barrel shaped dampenerset may delay the onset of buckling and inhibit fatigue damage to thedampener set.

Wear of the dampener sets may occur at the upper and lower outer edgesand/or at the upper and lower inner edges of the dampener sets. In someembodiments, the outer edges of the dampener sets may be rounded orchamfered to inhibit wear of the dampener sets. In some embodiments, theinner edges of the dampeners may be rounded or chamfered to inhibit wearof the dampeners. FIG. 41 depicts a cross-sectional embodiment ofdampener set 276 with chamfered ends 288.

In some embodiments, a conical washer design may be used to form thedampener set. Using conical washers may allow for large deformationswhile limiting the strain on the dampener material. FIG. 44 depicts across-sectional representation of stacked conical washers 290 that maybe used to form dampener set 276.

FIG. 28 depicts an embodiment of dynamic posterior stabilization system214. Dampener system 220 is an isolated dual dampener system. In anisolated dual dampener system, a first dampener set positioned betweenthe bone fasteners is compressed during extension, and little or noforce is applied to a second dampener set. The second dampener set iscompressed during flexion, and little or no force is applied to thefirst dampener set during flexion. The second dampener set may be longerthan the first dampener set if the allowable amount of flexion isgreater than the allowable amount of extension.

Dynamic posterior stabilization system may be coupled to a pair ofvertebra on a first side of the spine. When the patient laterally bendstowards the side on which dynamic posterior stabilization system iscoupled, the first dampener set is compressed. When the patientlaterally bends away from the side on which dynamic posteriorstabilization system is coupled, the second dampener set is compressed.

When the dampener system is secured to the first bone fastener, a shaftof the dampener system is fixed relative to the first bone fastener toinhibit rotational movement of the shaft. In some embodiments, the shaftis able to rotate relative to the second bone fastener to accommodateaxial rotation of vertebrae coupled to the dynamic posteriorstabilization system. In some embodiments, the vertical position of theshaft relative to the collar of the second bone fastener is variable sothat the dynamic posterior stabilization system is able to accommodateaxial rotation of vertebrae coupled to the dynamic posteriorstabilization system.

FIG. 45 depicts an exploded view of an embodiment of dampener system 220that is an isolated dual dampener system. Dampener system 220 is anin-line system. Dampener system 220 may include ball 292, elongatedmember 294, first dampener set 296, sleeve 298, second dampener set 300,and stop 302. Ball 292 may be positioned on a first threaded portion ofelongated member 294. In some embodiments, the threaded portion ofelongated member 294 may be less than 15 mm, less than 10 mm, less than7.5 mm or less than 5 mm in length.

Elongated member 294 may include stop 304. First dampener set 296 may bepositioned on elongated member 294 against stop 304. Sleeve 298 may beplaced on elongated member 294 against first dampener set 296. Elongatedmember 294 may be able to rotate relative to sleeve 298. Elongatedmember 294 may also be able to move axially relative to sleeve 298 tocompress first dampener set 296 or second dampener set 300 and allow forflexion/extension and/or lateral bending. Second dampener set 300 may bepositioned on elongated member 294 against sleeve 298. In someembodiments, the portions of dampener system 220 that contact dampenersets 296, 300 have spherical contours. Stop 302 may be secured toelongated member 294 against second dampener set 300. Stop 302 mayinclude threading that couples to a second threaded portion of elongatedmember 294. In some embodiments, stop 302 is permanently fixed toelongated member 294 by staking the threading.

When the assembled dampener system is attached to the bone fasteners ofthe dynamic posterior stabilization system, the patient may bepositioned in a neutral position with substantially no flexion,extension, or lateral bending. The position of ball 292 on the firstthreaded portion of elongated member 294 may be adjusted by rotating theball so that sleeve 298 fits in the collar of the second bone fastenerand the ball fits in the collar of the first bone fastener with littleno compression of first dampener set 296 or second dampener set 300.When the position of ball 292 is at the desired position, excess lengthof the shaft beyond the ball may be cut off and/or the further rotationof the ball on the shaft may be inhibited. The dampener system may becoupled to the bone fasteners (e.g., by closure members).

When elongated member 294 is coupled to the first bone fastener,translational and rotational movement of the elongated member relativeto the first bone fastener may be inhibited. When elongated member 294is coupled to the second bone fastener, translational and/or rotationalmovement of the elongated member relative to the second bone fastenermay be possible. The ability to have translational movement of elongatedmember 294 relative to the second bone fastener may allow isolated dualdampener system 220 to accommodate flexion, extension and lateralbending of a first vertebra coupled to the dynamic posteriorstabilization system relative to a second vertebra coupled to thedynamic posterior stabilization system. The ability to have rotationalmovement of elongated member 294 relative to the second bone fastenermay allow isolated dual dampener system 220 to accommodate axialrotation of vertebrae coupled to the dynamic posterior stabilizationsystem.

Elongated member 294 may be a rod, bar, plate, combination thereof, orother type of member coupled to the first bone fastener and the secondbone fastener. In some embodiments where the isolated dual dampenersystem is to be used with a dynamic interbody device, elongated member294 may be bent so that the elongated member has a curvature thatfacilitates the use of the isolated dual dampener system in conjunctionwith the dynamic interbody device. Elongated members with appropriatecurvature may be included in the instrument kit for the spinalstabilization procedure. In some embodiments, elongated members may bebent in the operating room. The instrument kit for the surgicalprocedure may include a bender.

FIG. 46 depicts an exploded view of an embodiment of dampener system220. Dampener system 220 is an isolated dual dampener system that may beoffset laterally from the second bone fastener. Dampener system 220 mayinclude ball 292, elongated member 294, first dampener set 296, washers306, offset member 308, second dampener set 300, and stop 302. Ball 292may be positioned on a first threaded portion of elongated member 294.

Elongated member 294 may include one or more flats 310. Flats 310 mayinteract with the walls that define elongated opening 312 in offsetmember arm 314 to inhibit rotation of elongated member 294 relative tooffset member 308. Elongated opening 312 may allow elongated member 294to move up or down when the elongated member is positioned through arm314 so that the dampener system is able to accommodate axial rotation ofvertebrae coupled to the dynamic posterior stabilization system. In someembodiments, a dampener may be positioned in the elongated member toprovide resistance to axial rotation.

Elongated member 294 may include stop 304. First dampener set 296 may bepositioned on elongated member 294 against stop 304. First washer 306′may be positioned against first dampener set 296. Offset member 308 maybe positioned against first washer 306′ and second washer 306″ may bepositioned against the offset member. Second dampener set 300 may bepositioned against second washer 306″ and stop 302 may be threaded on asecond threaded portion of elongated member 294 against the seconddampener set.

Surfaces 316 of washers 306′, 306″ that contact dampeners may bespherically contoured. Surfaces 316 may provide a large contact areabetween dampener sets 296, 300 and the washers. Other portions ofdampener systems that contact the dampeners may also have sphericallycontoured surfaces. The large contact area provided by the sphericalsurfaces may smooth out the contact stresses and reduce irregularcompression of the dampener sets. Washers 306 may inhibit extrusion ofdampener sets 296, 300 into opening 312 of offset member 308 when thedampener sets are compressed.

Offset member 308 may include collar connector 318 and cross link holder320. Collar connector 318 may be positioned over a collar of a bonefastener. A ball of a second dynamic posterior stabilization system maybe positioned in collar connector 318 to form a multi-level construct.In some embodiments, an offset member may be used when stabilizing asingle level. A closure member may be used to secure offset member 308to the bone fastener. If another stabilization system is needed for theadjacent level at a future date, the closure member positioned on thebone fastener may be removed and a ball of a dampener system for theadjacent level may be positioned in collar connector 318.

An end of a rod may be positioned in cross link holder 320. A set screwmay be threaded into the top portion of cross link holder 320 to securethe rod to offset member 308. A second end of the rod may be positionedin and secured to a cross link holder of a dynamic posteriorstabilization system positioned on an opposite side of the spine. Thecross link counteracts moments applied to the bone fastener because thedampener system is offset from the bone fastener.

Offset member 308 depicted in FIG. 46 may be used to form a dynamicposterior stabilization system that is offset laterally relative to thespine. The offset member of the dynamic posterior stabilization systempositioned on an opposite side of the spine may be a mirror image ofoffset member 308. FIG. 47 depicts offset member 308 that may be used ina dampener system to form a dynamic posterior stabilization system thatis offset medially relative to the second bone fastener. Cross linkholder 320 may be coupled to arm 314.

In some embodiments, offset member 308 in FIG. 46 is replaced with asleeve, such as sleeve 322 depicted in FIG. 48. Sleeve 322 allows forthe formation of an in-line dampener system. Sleeve 322 may be coupledto a second bone fastener, such as second bone fastener 218 depicted inFIG. 30. In other embodiments, an in-line dampener system is formedusing a sleeve shaped to fit in a collar such as the collar depicted inFIG. 29.

In some embodiments, the length of the dampener system is adjusted bysetting the position of a ball on a threaded portion of an elongatedmember. The ball is secured to the first bone fastener. In someembodiments, the portion of the dampener system that couples to thefirst bone fastener may be non-adjustable, and the portion of thedampener system that attaches to the second bone fastener may beadjustable. FIG. 49 depicts a cross-sectional representation of dampenersystem 220 wherein end 324 that attaches to the first bone fastener isnot adjustable. Dampener system 220 includes elongated member 294,sleeve 326, first dampener set 296, offset arm 314, second dampener set300, and stop 328.

Second dampener set 300 may be positioned against end 330 of sleeve 326.Offset arm 314 may be positioned against second dampener set 300. Firstdampener set 296 may be positioned against offset arm 314 and stop 328may be secured to sleeve 326 to inhibit removal of the first dampenerset, offset arm and second dampener set from the sleeve. In someembodiments, stop 328 may be welded to sleeve 326. A threaded portion ofsleeve 326 located in end 330 may be threaded on elongated member 294 sothat first dampener set 296 is positioned closest to end 324 of theelongated member. In some embodiments, offset arm 314 is a sleeve thatcouples to the second bone fastener to form an in-line dampener system.

A first bone fastener and a second bone fastener may be coupled tovertebrae. The length of the dampener system 220 may be adjusted byrotating sleeve 326. When the desired length is obtained, furtherrotation of the sleeve may be inhibited and excess portion of elongatedmember 294 may be removed before dampener system 220 is coupled to thebone fasteners.

FIG. 50 depicts an embodiment of dampener system 220 that uses setscrews to fix the position of dampener sets 296, 300 on elongated member294. Dampener sets 296, 300 and offset member 308 may be positioned onelongated member 294 between stops 332. In some embodiments, firstdampener set 296 may be adhered to offset member 308 or to first stop332′ to facilitate positioning the first dampener set. In someembodiments, second dampener set 300 may be adhered to offset member 308or to second stop 332″ to facilitate positioning the second dampenerset. The length of dampener system 220 may be set by moving stops 332along elongated member 294 so that offset member 308 is at a desiredposition relative to end 324. When the desired position is obtained, setscrews 334 may be threaded into stops 332 against elongated member 294to set the length of dampener system 220. If a portion of elongatedmember 294 extends beyond stop 332″, the portion may be removed. In someembodiments, a sleeve is substituted for offset member 308 to form anin-line dampener system.

When the dampener system of a dynamic posterior stabilization system iscoupled to the bone fasteners, the first bone fastener may be positionedin the lower vertebra of the vertebrae being stabilized, or in the uppervertebra of the vertebrae being stabilized. FIG. 51 depicts an in-lineversion of dynamic posterior stabilization system 214 at the S1-L5 levelsuch that first bone fastener 216 is positioned in upper vertebra 102(L5) and second bone fastener 218 is positioned in the lower vertebra104 (S1). A dynamic posterior stabilization system positioned so thatsecond dampener set 300 is the more caudal of dampener sets 296, 300 isin a non-inverted orientation.

FIG. 52 depicts laterally offset version of dynamic posteriorstabilization systems 214 coupled to vertebrae such that first bonefasteners 216 is positioned in lower vertebra 104 (L5) and second bonefasteners 218 are positioned in upper vertebra 102 (e.g., L4). Crosslink 336 secures first dynamic posterior stabilization system 214′ tosecond dynamic posterior stabilization system 214″. A dynamic posteriorstabilization system positioned so that first dampener set 296 is themore caudal of dampener sets 296, 300 is in an inverted orientation.

For some stabilization procedures, a two level stabilization system maybe installed. FIG. 53 depicts a two level stabilization system installedon one side of the spine. Dampener systems 220 are offset laterally, andthe dampener systems are in non-inverted orientations. Other dampenersystem embodiments allow for medial offset. Multi-level stabilizationsystems may be formed in inverted or non-inverted orientations.

In the embodiment of dynamic posterior stabilization system depicted inFIG. 28, dampener system 220 includes washers on each side of the collarof second bone fasteners 218. Convex contours of the washers may bepositioned in complementary concave recesses of the collar of the bonefastener. The convex contours may position dampener system 220 in thecollar of second bone fastener 218 and eliminate the need for thedampener system to include a sleeve positioned in the collar of thesecond bone fastener. The washers may be used to compress the dampenerwhen dampener system 220 is coupled to bone fasteners 216, 218.

FIG. 54 shows an embodiment of dampener system 220. Dampener system 220may include ball 292, elongated member 294, plate 338, dampener set 340,guide 342, pin 344, collar 346, and stop 302. Dampener set 340 may be asingle irregularly shaped dampener, or a separate flexion dampener and aseparate extension dampener positioned side by side. Plate 338 may bepositioned against a first end of dampener set 340. Flexion dampener 348of dampener set 340 may be coupled to elongated member 294. A firstportion of guide 342 may be secured to plate 338. Pin 344 may bepositioned through a slot in guide 342 and into collar 346. In someembodiments, pin 344 threads into collar 346.

Extension dampener 350 of dampener set 340 may be coupled to collar 346.A portion of elongated member 294 may pass through plate 338 and flexiondampener 348. Elongated member 294 may have first portion 352 with adiameter larger than the opening through the plate. A smaller diameterportion of elongated member 294 may pass through flexion dampener 348.Stop 302 may be secured to the end of elongated member 294 againstflexion dampener 348.

Ball 292 may be coupled to a threaded portion of elongated member 294.Ball 292 may be rotated to change the length of dampener system 220.When the desired length of dampener system 220 is set, rotation of ball292 may be inhibited and the ball may be positioned in the collar of afirst bone fastener positioned in a first vertebra. Collar 346 may besecured to a second bone fastener positioned in a second vertebra.During extension or lateral bending towards the side of the spine thatthe bone fasteners are coupled to, compression of extension dampener 350provides resistance to bending. First portion 352 of elongated member294 pushes against plate 338. Extension dampener 350 is compressedbetween plate 338 and collar 346. Interaction between pin 344 and guide342 accommodates reducing height of extension dampener 350. Stop 302remains the same distance away from plate 338 so that there is nocompression of flexion dampener 348.

During flexion and or lateral bending away from the side of the spinethat the bone fastener are coupled to, compression of flexion dampener348 provides resistance to bending. The first bone fastener moves awayfrom the second bone fastener. Stop 302 is drawn towards plate 338.Flexion dampener 348 is compressed between stop 302 and plate 338.Extension dampener 350 does not compress.

In some two level stabilization systems, positioning a bone fastener inthe middle vertebra may not be possible. Size considerations may makeextending the second dampener set beyond the second bone fastenerproblematic. An isolated dual dampener system with the dampener setslocated between the bone fasteners may be used for two levelstabilization system without a bone fastener positioned in the middlevertebra. FIG. 55 depicts an embodiment of dampener system 220. Dampenersystem 220 may include frame 354, first dampener set 296, seconddampener set 300, elongated member 294, and ball 292. Ball 292 may becoupled to a threaded portion of elongated member 294. The length ofdampener system 220 may be adjusted by rotating ball 292 to advance theball on the threaded portion of elongated member 294. When the desiredlength of dampener system 220 is set, further rotation of ball 292 maybe inhibited and excess length of elongated member 294 may be removed.

Frame 354 may include ball 356, shaft 358, support 360, first end 362,and second end 364. Ball 356 may be positioned in a bone fastener of thedynamic posterior stabilization system. Shaft 358 may be fixed to ball356 and first end 362. In some embodiments, a portion of shaft 358 mayextend through first end 362. The portion of shaft 358 that extendsthrough first end 362 may be positioned in an opening in first dampenerset 296 to position the first dampener set relative to support 360. Insome embodiments, first dampener set 296 is adhered to first end 362.

Support 360 connects first end 362 to second end 364. In someembodiments, support 360 is a wall that partially surrounds dampenersets 296, 300. In some embodiments, support 360 is formed of one or morebraces that support first end 362 and second end 364.

Elongated member 294 may include slide 366. Second dampener set 300 maybe placed against slide 366. The other end of elongated member may bepositioned through an opening in second end 364 of frame 354.

Ball 292 and ball 356 may be secured to bone fasteners positioned invertebrae (e.g., S1 and L4). During extension and/or lateral bendingtowards the side of the spine that the dynamic posterior stabilizationsystem is coupled to, the first bone fastener moves towards second bonefastener and slide 366 compresses first dampener set 296 against firstend 362. During flexion and/or lateral bending away from the side of thespine that the dynamic posterior stabilization system is coupled to, thefirst bone fastener moves away from the second bone fastener and 366compress second dampener set 300 against second end 364. Frame 354 mayrotate relative to elongated member 294.

For isolated dual dampener systems, the first dampener set is compressedduring extension while the second dampener set is not compressed. Also,the second dampener set is compressed during flexion while the firstdampener is not compressed. The length of the second dampener set may bereduced if both dampener sets are compressed during flexion and only thefirst dampener set is compressed during extension. Such a dampenersystem is a partially shared dual dampener system. In some embodiments,partially shared dual dampener systems are used to stabilize two levelsystems without a bone fastener positioned in the middle vertebra (e.g.,an L4-S1 stabilization system without a bone fastener secured to L5).

A dynamic posterior stabilization system with a partially shared dualdampener system is depicted in FIG. 56. Dynamic posterior stabilizationsystem 214 is an in-line, partially shared dual dampener system thatincludes bone fasteners 216, 218 and dampener system 220. Dynamicposterior stabilization system 214 is shown in a neutral position (i.e.,no added compression of dampener sets 296, 300). Dynamic posteriorstabilization system 214 may be installed in a non-inverted orientation(i.e., where bone fastener 216 is in an upper vertebra of the vertebraeto be stabilized) or in an inverted orientation (i.e., where bonefastener 216 is in a lower vertebra of the vertebrae to be stabilized).In some embodiments, the dampener system includes an offset member thatallows the dampener system to be offset laterally from the second bonefastener. In some embodiments, the dampener system includes an offsetmember that allows the dampener system to be offset medially from thesecond bone fastener. The use of dampener systems with offset membersmay allow for the formation of multi-level constructs.

FIG. 57 depicts the components of an in-line embodiment of dampenersystem 220. Dampener system 220 may include ball 292, first elongatedmember 368, second elongated member 370, washers 372, first dampener set296, second dampener set 300, sleeve 374, and stop 302. In someembodiments, the surfaces of washers 372 that contact dampener sets 296,300 are curved (e.g., spherically contoured).

First elongated member 368 may include threading 376, flat portion 378,first shoulder 380 and second shoulder 382. Threading 376 may complementthreading on the inside of ball 292. Second elongated member 370 mayinclude slot 384, groove 386, retainers 388, and threading 390. Flatportion 378 of first elongated member 368 may be placed in slot 384 ofsecond elongated member 370 to form a variable length elongated member.A protrusion in sleeve 374 may be positioned in groove 386. Retainers388 may provide a stop beyond which washer 372′ cannot pass on secondelongated member 370. Threading 390 may complement threading on theinside of stop 302.

Flat portion 378 may be placed in slot 384. First washer 372′ may beplaced on second elongated member 370 against retainers 388. Initially,slots 392 of first washer 372′ are aligned with first shoulder 380 offirst elongated member 368 to allow placement of the first washer onsecond elongated member 370. After slots 392 pass first shoulder 380,first washer 372′ may be rotated so that slots 392 do not align withfirst shoulder 380. First dampener set 296 may be positioned on secondelongated member 370 against first washer 372′. In some embodiments, thecentral passage of first dampener set 296 is shaped so that the firstdampener passes past second shoulder 382 of first elongated member 368.In other embodiments, first dampener is forced past first shoulder 380of first elongated member 368.

After first dampener set 296 is positioned against first washer 372′,second washer 372″ may be placed on second elongated member 370 againstthe first dampener set. Initially, slots 392 of second washer 372″ arealigned with first shoulder 380 of first elongated member 368 to allowplacement of the second washer on second elongated member 370. Aftersecond washer 372″ passes first shoulder 380, the second washer may berotated so that slots 392 do not align with the first shoulder.

Slots 394 in sleeve 374 may be aligned with first shoulder 380 of firstelongated member 368, and protrusion 396 may be oriented so that theprotrusion will fit in groove 386 of second elongated member 370. Sleeve374 may be placed on second elongated member 370 against second washer372″. Placement of protrusion 396 in groove 386 ensures that firstshoulder 380 is always aligned with slots 394 in sleeve 374.

Third washer 372′″ may be placed on second elongated member 370 againstsleeve 374. Third washer 372′″ may include slots 392 so that only onetype of washer is used to form dampener system 220. In some embodiments,third washer does not include slots. After third washer 372″′ ispositioned on second elongated member 370, second dampener set 300 maybe placed on the second elongated member against third washer 372′″.Stop may be rotated on threading 390 of second elongated member 370.When stop 302 is in a desired position, the stop may be welded orotherwise secured to second elongated member 370.

To insert the dynamic posterior stabilization system in a patient, thepatient is placed in a neutral position with substantially no flexion,extension, lateral bending or axial rotation. The first bone fastener issecured to the first vertebra of the vertebra to be stabilized. Thesecond bone fastener is secured to the second vertebra of the vertebrato be stabilized. The ball of the dampener system is adjusted so thatthe ball fits in the collar of the first bone fastener and the sleevefits in the collar of the second bone fastener with substantially noadditional compression of the dampener sets. After the ball is set tothe desired position on the elongated member, rotation of the ball maybe inhibited and any excess length of the elongated member may beremoved. The ball may be positioned in the collar of the first bonefastener, and sleeve may be positioned in the collar of the second bonefastener. A closure member may be secured to the collar of the firstbone fastener. The closure member attached to the collar of the firstmember may secure the ball in the collar and inhibit axial movement ofthe ball relative to the first bone fastener. In some embodiments, aclosure member is secured to the collar of the second bone fastener. Theclosure member secured to the second bone fastener may inhibit removalof the sleeve from the second bone fastener.

FIG. 58 depicts dynamic posterior stabilization system 214 with firstdampener 296 set compressed. During extension and/or during lateralbending towards the side of the spine to which the dynamic posteriorstabilization system is attached, first bone fastener 216 and secondbone fastener 218 move relatively closer together and compression offirst dampener set 296 resists relative movement of the bone fasteners.To compress first dampener set 296, sleeve 374 slides along secondelongated member 370 towards the first dampener set. Collar 222 ofsecond bone fastener 218 engages second washer 372″ and moves towardsfirst bone fastener 216. Movement of first washer 372′ is inhibited bysecond shoulder 382 of first elongated member 368. First dampener set296 is compressed between first washer 372′ and second washer 372″.Second dampener set 300 is uncompressed.

FIG. 59 depicts dynamic posterior stabilization system 214 with firstdampener 296 and second dampener set 300 compressed. During flexionand/or during lateral bending away from the side of the spine to whichdynamic posterior stabilization system 214 is attached, first bonefastener 216 and second bone fastener 218 move relatively away from eachother and compression of first dampener set 296 and second dampener set300 resists relative movement of the bone fasteners. To compress seconddampener set 300, sleeve 374 slides along second elongated member 370towards stop 302. Collar 222 of second bone fastener 218 engages thirdwasher 372′″ and compresses second dampener set 300 against stop 302. Tocompress first dampener set 296, second elongated member 370 slidesalong flat portion 378 of first elongated member 368 away from firstbone fastener 216. Retainers 388 engage first washer 372′ and draw firstwasher and first dampener set 296 towards second washer 372″. Firstshoulders 380 of first elongated member 368 inhibit movement of secondwasher 372″. First dampener set 296 is compressed between first washer372′ and second washer 372″.

FIG. 60 depicts an embodiment of dynamic posterior stabilization system214 with identical bone fasteners 216, 218 and in-line, partially shareddual dampener system 220 in a neutral position. FIG. 61 depicts anexploded view of dampener system 220 depicted in FIG. 60. Dampenersystem 220 may include ball 292, first elongated member 368, secondelongated member 370, keyed washer 372, first dampener set 296, firstkeyed linking washer 398, second keyed linking washer 400, washer 402,second dampener set 300, and stop 302.

First elongated member 368 may include threading 376, flat portion 378,first shoulder 380 and second shoulder 382. Threading 376 may complementthreading on the inside of ball 292. Second shoulder may provide a stopfor washer 372 on first elongated member 368.

Second elongated member 370 may include slot 384, retainers 388, flats404, and threading 390. Flat portion 378 of first elongated member 368may be placed in slot 384 of second elongated member 370 to form avariable length elongated member. Flats 404 may limit axial rotation ofsecond elongated member 368 when the elongated member is positioned in acollar of a bone fastener. Retainers 388 may provide a stop beyond whichwasher 372 cannot pass on second elongated member 370. Threading 390 maycomplement threading on the inside of stop 302.

Flat portion 378 may be placed in slot 384. Washer 372 may be placed onsecond elongated member 370 against retainers 388. Initially, slots 392of washer 372 are aligned with first shoulder 380 of first elongatedmember 368 to allow placement of the washer on second elongated member370. After slots 392 pass first shoulder 380, washer 372 may be rotatedso that slots 392 do not align with the first shoulder. First dampener296 may be positioned on second elongated member 370 against washer 372.In some embodiments, the central passage of first dampener set 296 isshaped so that the first dampener passes past first shoulder 380 offirst elongated member 368. In other embodiments, first dampener isforced past first shoulder 380 of first elongated member 368.

After first dampener set 296 is positioned against washer 372, firstkeyed linking washer 398 may be placed on second elongated member 370against the first dampener set. Initially, slots 392 of first keyedlinking washer 398 are aligned with first shoulder 380 of firstelongated member 368 to allow placement of the first keyed linkingwasher on second elongated member 370. First key linking washer 398 mayinclude tabs that are positioned to fit in slots 392 of second keyedlinking washer 400. Second keyed linking washer 400 may be placed onsecond elongated member 370 against first keyed linking washer 398.Initially, slots 392 of second keyed linking washer 400 are aligned withfirst shoulder 380. After second keyed linking washer 400 passes firstshoulder 380, first keyed linking washer 398 may be linked to the secondkeyed linking washer by rotating the second keyed linking washer and/orthe first keyed linking washer and placing tabs 406 of the second keyedwasher in slots 392 of the first keyed washer, and the tabs of the firstkeyed washer in slots 392 of the second keyed washer. Linking firstkeyed linking washer 398 to second keyed linking washer 400 inhibitsmovement of the linked washers past first shoulder 380.

Washer 402 may be placed on second elongated member 370. Second dampenerset 300 may be placed on second elongated member 370. Stop 302 may bethreaded on second elongated member 370. Stop 302 may be spiked, weldedor otherwise secured to second elongated member 370.

The surface of second keyed linking washer 400 that faces away fromfirst dampener set 296 may have a spherical contour. The sphericalcontour may complement a concave recess in the collar of the bonefastener that the dampener system is to be coupled to (e.g., concaverecess 244 depicted in FIG. 31). Similarly, the surface of washer 402that faces away from second dampener set 300 may have a sphericalcontour. The spherical contour may complement the concave surface in thecollar of the bone fastener that the dampener system is to be coupledto.

During insertion in a patient, the bone fasteners are positioned in thevertebrae to be stabilized. The appropriately sized dampener system isselected. The ball of the dampener system may be rotated to adjust thelength of the dampener system so that the ball fits in the collar of afirst bone fastener and the spherically contoured surface of the secondkeyed linking washer is positioned in the concave recess of the collarof the second bone fastener. The washer with the spherical contourpositioned next to the second dampener set may be used to compress thesecond dampener set against the stop so that the dampener system can bepositioned in the collar of the second bone fastener. Once the dampenersystem is positioned in the collar of the second bone fastener, thewasher may be released and closure members may be coupled to the bonefasteners to secure the dampener system to the bone fasteners.

During extension and/or lateral bending towards the side of the spine towhich the dynamic posterior stabilization system is attached, the firstbone fastener and second bone fastener move relatively closer together.Compression of the first dampener set resists relative movement of thebone fasteners towards each other. During flexion and/or lateral bendingaway from the side of the spine to which the dynamic posteriorstabilization system is attached, the first bone fastener and secondbone fastener move relatively farther apart. Compression of the firstdampener set and the second dampener set resist relative movement of thebone fasteners away from each other.

FIG. 62 depicts an embodiment of offset, partially shared dual dampenersystem 220 in a neutral position. Dampener system 220 may include ball292, elongated member 294, frame 408, first washer 372′, first dampenerset 296, second washer 372″, offset member 308, third washer 410, andsecond dampener set 300.

FIG. 63 depicts a cross-sectional representation of dampener system 220.Elongated member 294 may include first portion 412, second portion 414,and third portion 416. The diameter of second portion 414 is less thanthe diameter of first portion 412 and third portion 416. The diameter offirst portion 412 is smaller than the diameter of the opening throughfirst arm 418 of frame 408. The diameter of first portion 412 is greaterthan a diameter of the opening through first washer 372′ so that thefirst portion provides a stop for the first washer on elongated member294. The diameter of the opening through first washer 372′ is greaterthan the diameter of second portion 414. The length of second portion414 may be substantially the same length as the sum of the lengths offirst washer 372′, first dampener set 296 in the neutral position, andsecond washer 372″. The diameter of third portion 416 is greater than adiameter of the opening through second washer 372″ and less than adiameter of the opening through offset member 308. Third portion 416passes through third washer 410, second dampener set 300 and second arm420 of frame 408.

In the neutral position shown in FIG. 62, first arm 418 of the frame isadjacent to first washer 372′, and second arm 420 of frame 408 ispositioned on elongated member 294 adjacent to second dampener set 300.Ball 292 may be secured to a first bone fastener positioned in a firstvertebra. Offset member 308 may be secured to a second bone fastenerpositioned in a second vertebra.

The first bone fastener may move towards the second bone fastener whenthe vertebrae are subjected to extension and/or to lateral bendingtowards the side that dampener system 220 is coupled to. Compression offirst dampener set 296 provides resistance to such extension and/orlateral bending. First portion 412 of elongated member 294 engages firstwasher 372′ and moves the first washer towards second washer 372″.Second washer 372″ moves against offset member 308. First dampener set296 is compressed between first washer 372″ and second washer 372″.Third portion 416 of elongated member 294 slides outwards through secondarm 420 of frame 408 and does not compress second dampener set 300.

The first bone fastener may move away from the second bone fastener whenthe vertebrae are subjected to flexion and/or to lateral bending awayfrom the side that dampener system 220 is coupled to. Compression offirst dampener set 296 and second dampener set 300 provides resistanceto such flexion and/or lateral bending. When the first bone fastenermoves away from the second bone fastener, third portion 416 of elongatedmember 294 engages second washer 372″ and draws the second washertowards first washer 372′. Movement of first washer 372′ is stopped byfirst arm 418 of frame 408. First dampener set 296 is compressed betweenfirst washer 372′ and second washer 372″. Force applied to first arm 418by first washer 372′ moves frame 408 towards ball 292 and the first bonefastener and compresses second dampener set 300 between second arm 420and third washer 410. Third washer 410 pushes against offset member 308.

For some patients, space limitation or other considerations may requirethat the dampener sets of the dampener system not be located between thebone fasteners. FIG. 64 depicts an embodiment of dampener system 220 ina neutral position. Dampener system 220 is an in-line, partially shareddual dampener system. Dampener system 220 may include ball 292,elongated member 294, frame 422, washer 424, first dampener set 296,slide 426, second dampener set 300, and stop 302. Frame 422 may includesecond ball 356. Dampener sets 296, 300 of dampener system 220 areexternal to balls 292, 356 that couple to bone fasteners of the dynamicposterior stabilization system. In some embodiments, the surfaces ofwashers 424, slide 426 and other portions that contact dampener sets296, 300 are curved (e.g., spherically contoured).

Ball 292 may be positioned on a threaded portion of elongated member294. Rotation of ball 292 relative to elongated member 294 allows foradjustment of the distance between balls 292, 356. Ball 292 may berotated on elongated member 294 until the distance between balls 292,356 allows the balls to be positioned in collars of bone fasteners thatare secured to vertebrae. In some embodiments, further rotation of ball292 is inhibited once the desired distance between balls 292, 356 isestablished.

Elongated member 294 may have first portion 428 and a second portion(second portion 430 depicted in FIG. 65). The diameter of first portion428 is larger than the diameter of the second portion. A shoulder ispresent at the transition between first portion and the second portion.First portion 428 is sized slightly smaller than a passage in secondball 356 of frame 422. Openings through washer 424 and slide 426 aresized slightly larger than second portion 430, but smaller than firstportion 428. Washer 424 is positioned on elongated member 294 againstthe bottom of frame 422. First dampener set 296 is positioned againstwasher 424. Slide 426 is positioned against first dampener set 296 withprotrusions of the slide extending into slots in the arms of frame 422(shown in FIG. 65 and FIG. 66). Second dampener set 300 is positionedagainst slide 426, and stop 302 is secured to elongated member 294against the second dampener set.

FIG. 65 depicts dampener system 220 when first dampener set 296 iscompressed. Second ball 356 of frame 422 is moved towards ball 292.Washer 424 is positioned against the shoulder formed at the transitionbetween first portion 428 and second portion 430 of elongated member294. First dampener set 296 is compressed between washer 424 and slide426. Second dampener set 300 is uncompressed. First dampener set 296 maybe compressed as shown when dampener system 220 is coupled to bonefastener secured to vertebrae, and when the vertebrae are subjected toextension and/or to lateral bending towards the side of the spine thatthe dampener system is secured to.

FIG. 66 depicts dampener system 220 when first dampener set 296 andsecond dampener set 300 are compressed. Second ball 356 of frame 422 ismoved away from ball 292 along elongated member 294. Washer 424 ispositioned in the bottom of frame 422. Frame 422 moves toward stop 302and first dampener set is compressed between washer 424 and slide 426while second dampener set 300 is compressed between the slide and thestop. Dampener set 296, 300 may be compressed as shown when dampenersystem 220 is coupled to bone fastener secured to vertebrae, and whenthe vertebrae are subjected to flexion and/or to lateral bending awayfrom the side of the spine that the dampener system is secured to.

Partially shared dual dampener systems may be positioned on bonefastener so that the dampener sets are below the lower vertebra of thevertebrae to be stabilized (i.e., in a non-inverted orientation), or sothat the dampener sets are above the upper vertebra of the vertebrae tobe stabilized (i.e., in an inverted orientation). In some embodiments,the partially shared dual dampener system may include an offset memberthat allows the dampener system to be positioned medially or laterallyto the one or both of the bone fasteners. For example, a second ball maybe coupled to the side of the frame. An offset dual dampener system mayrequire a cross link to a dynamic posterior stabilization systempositioned on the opposite side of the spine.

For some patients, space limitations or other considerations may requirea single dampener set that is positioned between the bone fastenerfasteners of the dynamic posterior stabilization system. FIG. 67 depictsan embodiment of dynamic posterior stabilization system 214 withdampener system 220 in a neutral position. Dampener system 220 is asingle dampener system. While dual dampener systems allow for differentmaximum amounts of flexion and extension, single dampener system 220 mayallow for the same maximum amount of flexion and extension. Dualdampener systems and single dampener systems may provide for increasingresistance to flexion/extension and/or lateral bending with increasedbending. In some embodiments, the dynamic interbody device or devicesused in conjunction with the dynamic posterior stabilization system orsystems set the maximum amount of flexion/extension and/or lateralbending of stabilized vertebrae. In some embodiments, the dynamicposterior stabilization systems set the maximum amount offlexion/extension and/or lateral bending of stabilized vertebrae. Insome embodiments, single dampener systems are used to stabilize twolevel systems without a bone fastener positioned in the middle vertebra(e.g., an L4-S1 stabilization system without a bone fastener secured toL5).

FIG. 68 depicts the components of an offset embodiment of singledampener system 220. Single dampener system 220 may include ball 292,first elongated member 368, second elongated member 370, washers 372,dampener set 432, offset member 308, and end piece 434. Dampener set 432may be compressed during flexion, extension and lateral bending. Toaccommodate compression of dampener set 432, the length of the elongatedmember formed by first elongated member 368 and second elongated member370 changes. In some embodiments, the surfaces of washers 372 thatcontact dampener set 432 are curved (e.g., spherically contoured).

First elongated member 368 may include threading 376, flat portion 378,first shoulder 380 and second shoulder 382. Threading 376 may complementthreading on the inside of ball 292. Second elongated member 370 mayinclude slot 384, retainers 388, and threading 390. Flat portion 378 maybe placed in slot 384 to form a variable length elongated member.Retainers 388 may provide a stop beyond which washer 372′ cannot pass onsecond elongated member 370. Threading 390 may complement threading onthe inside of end piece 434.

First washer 372′ may be placed on second elongated member 370.Initially, slots 392 of first washer 372′ are aligned with firstshoulder 380 of first elongated member 368 to allow placement of thefirst washer on second elongated member 370. After slots 392 pass firstshoulder 380, first washer 372′ may be rotated so that slots 392 do notalign with first shoulder 380. First washer 372′ may be placed againstretainer 388. Retainer 388 is sized larger than the central opening infirst washer 372′. After first washer 372′ is positioned on secondelongated member 370, dampener set 432 may be positioned on the secondelongated member against the first washer. In some embodiments, thecentral passage of dampener set 432 is shaped so that the dampener setpasses past first shoulder 380 of first elongated member 368. In otherembodiments, dampener set 432 is forced past first shoulder 380 of firstelongated member 368.

After dampener set 432 is positioned, second washer 372″ may be placedon second elongated member 370 against the dampener set. In someembodiments, second washer 372″ may be truncated or cut to accommodatespatial limitations due to offset member 308. In other embodiments,(e.g., for in-line embodiments of single dampener systems) truncated orcut second washers may not be required. Initially, slot 392 of secondwasher 372″ is aligned with first shoulder 380 of first elongated member368 to allow placement of the second washer on second elongated member370. After slot 392 passes first shoulder 380, second washer 372″ may berotated so that the slot does not align with the first shoulder.

The end of second elongated member 370 may be positioned through opening312 of offset member 308. End piece 434 may be threaded onto threading390 of second elongated member 370. The outer surface of end piece 434may be spherically contoured and the surface of offset member 308 thatthe outer surface contacts may also be spherically contoured. Slots 436of end piece 434 extend through opening in offset member 308. Slots 436of endpiece 434 may be oriented so that first shoulder 380 of firstelongated member 368 align with the slots.

To insert the assembled dynamic posterior stabilization system in apatient, the patient is placed in a neutral position with substantiallyno flexion, extension, lateral bending or axial rotation. The first bonefastener is secured to the first vertebra of the vertebra to bestabilized. The second bone fastener is secured to the second vertebraof the vertebra to be stabilized. The ball of the dampener system isadjusted so that the ball fits in the collar of the first bone fastenerand offset member fits on the second bone fastener with substantially nocompression of dampener set. The ball may be positioned in the collar ofthe first bone fastener, and the sleeve may be positioned in the collarof the second bone fastener. Closure members may be secured to thecollars of the first bone fastener and the second bone fastener.

FIG. 69 depicts dynamic posterior stabilization system 214 compressed asif vertebrae coupled to first bone fastener 216 and second bone fastener218 were subjected to extension and/or lateral bending towards the sidethat the dynamic posterior stabilization system is coupled to. In someembodiments, second washer 372″ is positioned against offset member 308and second shoulder 382 of first elongated member 368 contact firstwasher 372′ and move the first washer towards second bone fastener 218to compress dampener set 432. In some embodiments, an end of firstelongated member 368 contacts the bottom of the slot in the secondelongated member and pushes the second elongated member towards secondbone fastener 218 such that end piece 434 moves away from offset member308.

FIG. 70 depicts dynamic posterior stabilization system 214 extended asif vertebrae coupled to first bone fastener 216 and second bone fastener218 were subjected to flexion and/or lateral bending away from the sidethe dynamic posterior stabilization system is coupled to. Firstelongated member 368 moves away from second elongated member 370. Endpiece 434 contacts offset member 308 and first shoulder 380 of firstelongated member 368 contacts and draws second washer 372″ towardsretainers 388 to compress dampener set 432 between first washer 372′ andsecond washer 372″. Movement of first washer 372′ is stopped byretainers 388.

For in-line dampener system embodiments, the end piece may be a sleevethat is coupled to the second elongated member. The second elongatedmember may include a stop (e.g., a flared end) that inhibits removal ofthe sleeve from the second elongated member. The sleeve allows a portionof the second elongated member to move through the collar when the firstbone fastener moves closer to the second bone fastener. Movement of thesecond elongated member through the sleeve is resisted by compression ofthe dampener set. The stop allows the first elongated member to moveaway from the second elongated member when the first bone fastener movesaway from the second bone fastener. Movement of the first elongatedmember away from the second elongated member is resisted by compressionof the dampener set.

FIG. 71 depicts an embodiment of dampener system 220 in a neutralposition. Dampener system 220 has a single dampener and an externalframe. Dampener system 220 may include ball 292, elongated member 294,offset member 308, first washer 372′, dampener set 432, and secondwasher 372″. In some embodiments, the surfaces of washers 372 thatcontact dampener set 432 are curved (e.g., spherically contoured).

FIG. 72 depicts a cross-sectional representation of dampener system 220.Elongated member 294 may include first portion 412, second portion 414,and third portion 416. The diameter of second portion 414 is less thanthe diameter of first portion 412 and third portion 416. The diameter offirst portion 412 is smaller than the diameter of the opening throughfirst arm 438 of offset member 308. The diameter of first portion 412 isgreater than a diameter of the opening through first washer 372′ so thatthe first portion provides a stop for the first washer on elongatedmember 294. The diameter of the opening through first washer 372′ isgreater than the diameter of second portion 414. The length of secondportion 414 may be substantially the same length as the sum of thelengths of first washer 372′, dampener set 432 in a neutral position,and second washer 372″. The diameter of third portion 416 is greaterthan a diameter of the opening through second washer 372″ and less thana diameter of the opening through second arm 440 of offset member 308.The diameter of the opening through second washer 372″ is greater thanthe diameter of second portion 414.

Ball 292 may be secured to a first bone fastener positioned in a firstvertebra. Offset member 308 may be secured to a second bone fastenerpositioned in a second vertebra. The first bone fastener may movetowards the second bone fastener when the vertebrae are subjected toextension and/or to lateral bending towards the side that dampenersystem 220 is coupled to. Compression of dampener set 432 providesresistance to such extension and/or lateral bending. First portion 412of elongated member 294 engages first washer 372′ and moves the firstwasher towards second washer 372″. Dampener set 432 is compressedbetween first washer 372″ and second washer 372″. Third portion 416 ofelongated member 294 slides outwards through second arm 440 of offsetmember 308.

The first bone fastener may move away from the second bone fastener whenthe vertebrae are subjected to flexion and/or to lateral bending awayfrom the side that dampener system 220 is coupled to. Compression ofdampener set 432 provides resistance to such flexion and/or lateralbending. When first bone fastener moves away from second bone fastener,third portion 416 of elongated member 294 engages second washer 372″ anddraws the second washer towards first washer 372′ to compress dampenerset 432 between the first washer and the second washer.

FIG. 73 depicts an embodiment of dampener system 220 in a neutralposition. Dampener system 220 is an in-line, single dampener system withtwo elongated members. Dampener system 220 may include first elongatedmember 368, first ball 292, second elongated member 370, second ball356, first washer first washer 372′, dampener set 432, and second washer372″. First ball 292 may be placed on a threaded portion of firstelongated member 368. First ball 292 may be rotated to adjust the lengthof dampener system 220. In other embodiments, second ball 356 or bothballs may allow for adjustment of the length of the dampener system. Insome embodiments, the surfaces of washers 372 that contact dampener set432 are curved (e.g., spherically contoured).

FIG. 74 depicts the components of single dampener system 220 depicted inFIG. 73. Elongated member 368 may include first shoulder 442, secondshoulder 444, and stop 446. Second elongated member 370 may includefirst shoulder 448, second shoulder 450 and stop 452. Washers 372′, 372″may include slots 454 that allow for passage of the shoulders ofelongated members 368, 370.

First washer 372′ may be oriented so that slots 454 allow the firstwasher to pass beyond first shoulder 442 of elongated member 368. Firstwasher 372′ may be moved past first shoulder 442, rotated 90°, andpositioned against second shoulder 444. Dampener set 432 may bepositioned on first elongated member 368 against first washer 372′.Second washer 372″ may be placed on first elongated member 368 againstdampener set 432 and the second washer may be rotated 90°. Second shaft370 may be oriented so that first shoulder 448 passes through slots 454of second washer 372″ and first washer 372′. First shoulder 448 may bepushed through second washer 372″, dampener set 432, and first washer372′. When first shoulder 448 passes through first washer 372′, thefirst washer and second washer 372″ may be rotated (e.g., about 45°) sothat removal of elongated members 368, 370 from the washers isinhibited.

Balls 292, 356 of assembled dampener system 220 shown in FIG. 73 may besecured to bone fasteners positioned in vertebrae. During extensionand/or lateral bending towards the side of the vertebrae the dampenersystem is coupled to, the bone fasteners move closer together andcompression of dampener set 432 provides resistance to the movement.Second shoulder 444 of first elongated member 368 moves first washer372′ towards second washer 372″ and second shoulder 450 of secondelongated member 370 moves the second washer towards the first washer tocompress dampener set 432. In some embodiments, the range of motion offirst elongated member 368 relative to second elongated member 370 islimited by contact of first shoulder 442 with stop 452. In someembodiments, the range of motion of second elongated member 370 relativeto first elongated member 368 is limited by contact of first shoulder448 with stop 446. In some embodiments, the range of motion of firstelongated member 368 relative to second elongated member 370 is limitedby the maximum amount of compression allowed by dampener set 432.

During flexion and/or lateral bending away from the side of thevertebrae the dampener system is coupled to, the bone fasteners movefarther apart and compression of dampener set 432 provides resistance tothe movement. First shoulder 442 of first elongated member 368 movessecond washer 372″ towards first washer 372′, and first shoulder 448 ofsecond elongated member 370 moves the second washer towards the firstwasher to compress dampener set 432.

FIG. 75 depicts a representation of dynamic interbody device 100 andposterior stabilization system 214 positioned between vertebrae 102,104. Bridge 456 may be coupled to second bone fastener 218 of dynamicposterior stabilization system 214. Bridge 456 may inhibit undesiredmigration of dynamic interbody device 100 relative to vertebrae 102, 104while still allowing for flexion, extension, lateral bending, and/oraxial rotation of the vertebrae.

In some embodiments, the center of curvature of the elongated member ofdampener system 220 of dynamic posterior stabilization system 214 mayalign or substantially align with the center of curvature of dynamicinterbody device 100 that allows for flexion/extension and/or lateralbending. Aligning or substantially aligning the center of curvature ofthe elongated member with the center or centers of curvature of dynamicinterbody device 100 allows the elongated member to move relative tosecond bone fastener 218 during flexion/extension and/or lateral bendingso that dynamic posterior stabilization system 214 works in conjunctionwith the dynamic interbody device. In some embodiments, the curvature ofthe elongated member of dampener system 220 of dynamic posteriorstabilization system 214 may substantially follow the desired curvatureof the spine.

Dynamic posterior stabilization system 214 may share a portion of theload applied to the vertebrae 102, 104 while providing guidance andresistance to flexion/extension and/or lateral bending that is, or isapproximate to, the resistance provided by a normal functional spinalunit. Allowing for movement of the dynamic interbody device and formovement of the dynamic posterior stabilization system may inhibitdeterioration of adjacent functional spinal units.

Bridge 456 may couple dynamic interbody device 100 to dynamic posteriorstabilization system 214. Bridge 456 may be coupled to dynamic posteriorstabilization system 214 at or near to second bone fastener 218.Coupling bridge 456 to dynamic posterior stabilization system 214 at ornear to second bone fastener 218 may inhibit or eliminate contact of thebridge with neural structure exiting from between the vertebrae.

In some embodiments, a posterior approach may be used to install astabilization system for a patient. The stabilization system may replaceone or more parts of a functional spinal unit of the patient. Thestabilization system may include one or more dynamic interbody devices,and one or more dynamic posterior stabilization systems.

During some posterior insertion procedures, the facet joints at theoperative level may be removed (e.g., the superior facets from lowervertebra and the inferior facets from the upper vertebra). In someembodiments, the spinous process of the upper vertebra may also beremoved. A bone awl may be used to mark each of the pedicles where thebone fasteners are to be positioned. A pedicle probe may be used towiden the initial holes made by the bone awl and set a desiredtrajectory. A tap may be attached to a handle and inserted into one ofthe pedicles. After insertion, the handle may be removed leaving the tapextending from the pedicle. The handle and the tap may have an AOconnection or other type of low profile connection system. A tap may beinserted in each of the four pedicles. The taps may remain in thepedicles. Initially, the taps may be used to maintain distraction duringa discectomy to provide disc space for the dynamic interbody devices.FIG. 76 depicts taps 458 positioned in lower vertebra 104, with thehandle removed from the taps. Taps 458 may be positioned at any desiredangle into lower vertebra 104 and the upper vertebra.

After a discectomy, two expandable trials may be inserted in the discspace between the vertebrae. The expandable trial used on the left sideof the patient may be a mirror image of the expandable trial used on theright side of the patient. FIGS. 77-79 depict an embodiment ofexpandable trial 460 that may be positioned on a first side of thevertebrae. Each expandable trial may include body 462, rotator 464,scale 466, base plate 468 and movable plate 470. Rotator 464 may belocated at an end of body 462. Scale 466 may be located in an upperportion of body 462.

A rotatable handle may be coupled to rotator 464. When rotator 464 isturned, movable plate 470 moves in or out relative to base plate 468.FIG. 78 depicts movable plate 470 extended away from base plate 468. Theamount of movement of movable plate 470 relative to base plate 468 maybe indicated by the change in position of a movable portion of scale 466relative to a stationary portion of the scale. The movable portion mayinclude numbers and markings that indicate the height of a correspondingdynamic interbody device. The marking and corresponding number thataligns with a marking of the stationary portion of the scale indicatesthe current separation height of movable plate 470 relative to baseplate 468.

A middle portion of body 462 may include passage 472, keyway 474, andguide recess 476. A drill or other type of cutter may be positionedthrough passage 472 to form a groove in the lower vertebra toaccommodate a keel of the dynamic interbody device to be positioned inthe disc space between the vertebrae. Keyway 474 may ensure that onlythe proper instrument guide can be used in association with theparticular expandable trial. Guide recess 476 may accept an end of aguide release of the proper guide.

Base plate 468 may have an inferior surface with a shape that issubstantially the same as the shape of the inferior surface of thedynamic interbody device to be positioned between the vertebrae withouta keel. Base plate 468 may be positioned against the lower vertebra ofthe vertebrae being stabilized. Movable plate 470 may have a superiorsurface with a shape that is substantially the same as the shape of thesuperior surface of the dynamic interbody device to be positionedbetween the vertebrae. When the expandable trial is in an initialposition, the movable plate and the base plate have a height that allowsfor insertion in the disc space between the vertebrae. After insertion,the rotator may be turned to separate the movable plate from the baseplate to position the base plate against the lower vertebra and themovable plate against the upper vertebra.

The base plate and movable plate of the expandable trials may bepositioned in the disc space between the vertebrae. An engaging end of ahandle may be inserted in the rotator of a first expandable trial. Thehandle may be turned to cause the movable plate to move away from thebase plate so that the movable plate and the base plate contact thevertebrae. The handle may be used to rotate the rotator of the secondexpandable trial so that the movable plate and the base plate of thesecond expandable trial contact the vertebrae. The separation heightbetween the base plate and the movable plate is indicated by the scaleof the expandable trial.

Guides may be coupled to each expandable trial. FIGS. 80-82 depict anembodiment of guide 478. Guide 478 may include passageway 480, guiderelease 482, passage 484, and recess 486. Passageway 480 may include key488. Passageway 480 is shaped to fit over the body of the properexpandable trial. The key of the proper expandable trial fits in keyway488. Passage 484 accepts posts of a bridge that couples the firstexpandable trial to the second expandable trial. Recess 486 accommodatesa stabilizer of the bridge.

Guide release 482 may include grip 490, body 492, and end 494. When grip490 is pulled outward from the guide 478, the grip may be rotatedrelative to body 492. In a first position (depicted in FIG. 81), end 494of guide release extends into passageway 480. Arms 496 of grip 490 arenext to flats 498 of body 492. A spring or other bias member in guiderelease 482 drives end 494 into passageway 480. In a second position(depicted in FIG. 82), end 494 does not extend into passageway 480. Grip490 is pulled away from passageway 480 and rotated so that arms 496 ofthe grip reside on the top of body 492. The second position may be usedto facilitate removal of an expandable trial or insertion instrumentfrom guide 478.

A first guide may be placed over the appropriate expandable trial andlowered until the key of the guide is in the keyway of the expandabletrial and the end of the guide release inhibits further movement of theguide. The grip may be pulled outwards to withdraw the end of the guiderelease from the passageway. The guide may be lowered and the grip maybe released so that the spring in the guide release forces the end ofthe guide release against the body of the expandable trial. The guidemay be lowered until the end of the guide release extends into the guiderecess of the expandable trial. A second guide may be placed over theother expandable trial. Attaching the guides to the expandable trialsafter insertion of the base plates and movable plates between thevertebrae may allow more visibility of the position of the base platesand movable plates of the expandable trials during insertion. Duringsome dynamic interbody device insertion procedures, the guide for thefirst expandable trial and/or the guide for the second expandable trialis placed on the appropriate expandable trial before the base plate andmovable plate of the expandable trial is positioned between thevertebrae.

The position of the expandable trials may be adjusted so that thepassages of the guides are oriented vertically. Also, an end of the baseplate of the first expandable trial may touch or be close to touching anend of the base plate of the second expandable trial. In someembodiments, the base plates of the expandable trials may be coupledtogether with male and female portions when the base plates arepositioned between the vertebrae.

Posts of the bridge may be inserted in the passages of the guides. FIG.83 depicts an embodiment of insertion bridge 500. Insertion bridge 500may include handle 502, posts 504, and wheel 506. Handle 502 facilitatespositioning and moving insertion bridge 500. Handle 502 may includeslide 508 with threaded opening 510. Slide 508 may move forward andbackward in handle 502. Posts 504 may fit within passages of the guides.Wheel 506 may extend or retract stabilizers 512. Stabilizers 512 mayextend from the body of insertion bridge 500 into the recesses of theguides. FIG. 84 depicts stabilizers 512 extended from the body ofinsertion bridge 500. When the stabilizers 512 are extended against therecesses of the guides, the outward force applied by the stabilizers tothe guides generates torque applied by the guide to posts 504. Theoutward force and the torque couple the guides to insertion bridge 500so that the guides remain coupled to the bridge when the expandabletrials are removed from the guides.

FIG. 85 depicts insertion bridge 500 coupled to guides 478′, 478″. Wheel506 has been turned to extend the stabilizers into the recesses of theguides and couple guides 478′, 478″ to insertion bridge 500.

A bar assembly may be coupled to the slide of the insertion bridge. FIG.86 depicts bar assembly 514 coupled to insertion bridge 500. Barassembly 514 may include base 516, knob 518, and rods 520. A shaftcoupled to knob 518 may extend through base 516. A threaded end of theshaft may be threaded into the threaded opening in the slide ofinsertion bridge 500. Rods 520 may be coupled to the base 516. Rods 520may be positioned near taps 458 by sliding the slide relative to handle502 and/or by rotating rods 520 relative to the taps. When rods 520 arepositioned near taps 458, knob 518 may be tightened against base 516 toinhibit movement of the slide relative to handle 502 and to inhibitrotation of the rods relative to the taps.

Rod connectors may be attached to the taps and to the rods of the barassembly to anchor the insertion bridge to the spine. FIG. 87 depictsrod connector 522 attached to tap 458 and rod 520. When tap 458 and rod520 are snapped into the openings of rod connector 522, knob 524 of therod connector may be tightened to secure the taps and rods together. Asecond rod connector may be used to secure the second tap to the secondrod.

The rotatable handle may be inserted into the rotators of the expandabletrials and turned to set the expandable trials to the height of thedynamic interbody devices to be placed in the disc space. A keel guidemay be inserted in the passage of the first expandable trial. FIG. 87also depicts keel guide 526 positioned in passage 472 of expandabletrial 460′. FIG. 88 depicts a distal portion of keel guide 526 withdrill bit 528 forming a groove in lower vertebra 104. Base plate 468 ofexpandable trial includes a concave groove that accommodates drill bit528. After the formation of the first keel groove, drill bit 528 andkeel guide 526 may be removed from the first expandable trial. The keelguide may be placed in the passage of the second expandable trial. Thedrill bit may be used to form a second keel groove in the lowervertebra.

The dynamic interbody devices to be inserted between the vertebrae maybe attached to the appropriate insertion instruments. FIG. 89 depictsinsertion instrument 530′ for the first dynamic interbody device. Theinsertion instrument for the second dynamic interbody device may be amirror image of the insertion instrument for the first dynamic interbodydevice. Insertion instrument 530 may include key 532, guide recess 534,wheel 536, shaft 538, and ridges 540. Key 532 and the shape of the bodyof insertion instrument 530 correspond to the shape of the passagewaythrough the appropriate guide. Guide recess 534 accepts the end of theguide release of the guide to fix the position of insertion instrument530 relative to the guide.

Wheel 536 may be rotated to rotate shaft 538. Rotating shaft 538 mayadvance or retract the shaft relative to the body of insertioninstrument 530. The end of shaft 538 may be threaded. The threaded endmay mate with the threaded opening in the appropriate dynamic interbodydevice. When shaft 538 is threaded to the appropriate dynamic interbodydevice, ridges 540 reside in the slots of the dynamic interbody deviceto place the dynamic interbody device in the desired position forinsertion (i.e., neutral axial rotation, neutral lateral bending, andfull flexion).

The rotation handle may be attached to the rotator of the firstexpandable trial. The rotator may be turned to decrease the separationheight between the base plate and the movable plate of the expandabletrial. The grip of the guide release may be pulled outwards, rotated andreleased so that the end of the guide release is withdrawn from thepassageway of the guide. The first expandable trial may be removed fromthe guide. The first dynamic interbody device may be placed through thepassageway and between the vertebrae. The grip of the guide release maybe pulled outwards, rotated and released so that the spring of the guiderelease tries to force the end of the guide release into the passagewayof the guide. The insertion instrument may be driven downwards until theend of the guide release snaps into the guide recess of the insertioninstrument. If needed, a mallet or other impact instrument may be usedagainst the insertion instrument to drive the dynamic interbody devicebetween the vertebrae.

The second expandable trial may be removed from the guide. The seconddynamic interbody device may be inserted between the vertebrae. FIG. 90depicts insertion instruments 530′, 530″ and dynamic interbody devices100′, 100″ positioned against lower vertebrae 104. Imaging techniquesmay be used to determine that the dynamic interbody devices are properlyinterconnected and positioned in the disc space. When the dynamicinterbody devices are properly interconnected and positioned, wheels 536of insertion instruments 530′, 530″ may be rotated to disconnect theinsertion instruments from dynamic interbody devices 100′, 100″. Grips490 of guides 478′, 478″ may be pulled outwards to retract the ends ofthe guide releases from the passageways of the guides, and insertioninstruments 530′, 530″ may be removed from the guides. Rod connectors522 may be removed from taps 458 and bars 520. Insertion bridge 500,with bar assembly 514 and guides 478, may be removed.

Taps 458 may be removed from the vertebrae and bone fasteners of dynamicposterior stabilization systems may be inserted in the openings wherethe taps where positioned. A length of a dampener system of a firstdynamic posterior stabilization system may be adjusted so that thedampener system can be coupled to the bone fasteners. The dampenersystem may be secured to the bone fasteners to form the first dynamicposterior stabilization system. A length of a dampener system of asecond dynamic posterior stabilization system may be adjusted so thatthe dampener system can be coupled to the bone fasteners. The dampenersystem may be coupled to the bone fasteners to form the second dynamicposterior stabilization system. If needed, a cross link may be coupledto the first dynamic posterior stabilization system and the seconddynamic posterior stabilization system.

In some embodiments, another technique may be used to insert dynamicinterbody devices between vertebrae. An insertion structure may beformed before positioning an expandable trial or expandable trialsbetween the vertebrae. Taps may be inserted in each of the pedicles.FIG. 76 depicts taps 458 positioned in lower vertebra 104, with thehandle removed from the taps. Taps 458 may be positioned at any desiredangle into lower vertebra 104 and the upper vertebra.

After a discectomy, one or more trials may be positioned in and removedfrom the disc space on a first side and a second side of the vertebrae.The trials may have the same length and width profile as the firstmember of the dynamic interbody device to be placed in the disc space orthe same length and width profile as the third member of the dynamicinterbody device to be placed in the disc space. The lengths and widthsof the dynamic interbody devices to be placed in the disc space may bedetermined based on the trials.

During some insertion procedures, the position of lower vertebra 104 isused as the basis for establishing the insertion angles for the dynamicinterbody devices. A support frame may be coupled to taps 458. FIG. 91depicts support frame 542 coupled to taps 458. Support frame 542 mayinclude rod connectors 522, bar assembly 514, and bridge assembly 544.Bar assembly 514 may include a shaft with a threaded end, hub 516, knob518, and rods 520. Rods 520 may be directly connected to hub 516 so thatrotation of the rods independent of the hub is inhibited.

Rod connectors 522 may be used to couple bar assembly 514 to taps 458.Tap connectors 522 have sufficient freedom of movement to allow barassembly 514 to be positioned at a desired height above the vertebraewith a horizontal orientation and with the vertical center line of thebridge assembly positioned substantially in line with the verticalcenter line of the end plate of lower vertebra 104. Hub 516 may berotated in a recess in the handle of bridge assembly 544 to allow thefront face of the bridge assembly to be oriented substantially parallelto the end plate of lower vertebra 104. Hub 516 may be moved forward orbackward in the recess to adjust the offset distance of the front faceof bridge assembly 544 from the end plate of lower vertebra 104.

Bridge assembly 544 may include handle 502, slide 508, guide slots 546,and guide releases 548. Handle 502 may be used to move bridge assembly544. Slide 508 may be positioned in a hollow portion of handle 502. Hub516 of bar assembly 514 may be positioned in a recess in handle 502. Thethreaded end of the shaft of bar assembly 514 may be threaded into athreaded opening of slide 508. When knob 518 of bar assembly 514 isloose, the bar assembly may be adjusted back and forth in the recess ofhandle to change the offset position of the front face of bridgeassembly 544 relative to lower vertebra 104. Also, the orientation ofthe front face of bridge assembly 544 relative to the end plate of thelower vertebra may be changed by rotating handle 502 relative to hub516. Knob 518 may be tightened to fix the position of bar assembly 514relative to the handle 502. When bridge assembly 544 is properlypositioned, the front face of the bridge assembly may be substantiallyparallel to the endplate of bottom vertebra 104, and guide slots 546 aresubstantially vertical and equidistant from the vertical centerline oflower vertebra 104.

Protrusions of instrument guides may be positioned in guide slots 546.Guide releases 548 may include a spring or other bias member thatextends an end of the guide release beyond the front face of the bridgeassembly. The end of the guide release may extend into an opening of aninstrument guide to couple bridge assembly 544 to the instrument guide.A grip may be pulled away from bridge assembly 544 to retract the end ofguide release 546 and allow the instrument guide to be removed from thebridge assembly.

A first guide and a second guide may be placed in guide slots 546 ofbridge assembly 544. The first guide may be a mirror image of the secondguide. When the guides are fully inserted in the guide slots of bridgeassembly 544, guide releases 548 inhibit movement of the guides. Duringsome procedures, guides are positioned in guide slots 546 before thesupport frame is coupled to the taps.

FIG. 92 depicts a perspective view of first instrument guide 478′ usedon a first side of the bridge assembly. First instrument guide 478′ mayinclude protrusion 550, opening 552, passageway 480, key 488, and guiderelease 482. Protrusion 550 may be placed in a guide slot guide slot ofthe bridge assembly. Protrusion 550 may be angled relative to passageway480 so that the passageway is at a desired angle relative to vertical(and the lower vertebra) when the protrusion is positioned in the guideslot of the bridge assembly. In some embodiments, the angle ofpassageway 480 of the first guide 478′ and the angle of the passagewayof the second guide are directed inwards toward the vertical center lineof the lower vertebra at about 15° relative to vertical. In someembodiments, the angle of passageway 480 of the first guide 478′ and theangle of the passageway of the second guide are directed inwards towardthe vertical center line of the lower vertebra at about 12° relative tovertical. When protrusion 550 is inserted in the guide slot of thebridge assembly, the end of the bridge assembly guide release extendsinto opening 552 to inhibit undesired movement of first guide 478′.

A trial or inserter may be placed through passageway 480 of first guide478′ that is positioned in the bridge assembly. Passageway 480 mayinclude key 488. Key 488 may fit in a keyway of an appropriate trial orinserter used with the first guide 478′. When the appropriate trial orinserter is positioned in first guide 478′, a spring or other biasmember of guide release 482 may extend an end of the trial release intoan opening in the trial or inserter to inhibit movement and allow a userto know that the trial or inserter is fully inserted.

FIG. 93 depicts an embodiment of first expandable trial 460′ that may beused to determine the appropriate height of a dynamic interbody deviceto be positioned between vertebrae. First expandable trial 460′ may beused in conjunction with the first guide. A second expandable trial,which may be a mirror image of first expandable trial 460′, may be usedin conjunction with the second instrument guide. Expandable trial 460′may include body 462, keyway 474, guide recess 476, rotator 464, scale466, base plate 468 and movable plate 470. Keyway 474 may extend along aportion of body 462. When expandable trial 460′ is inserted into thefirst guide, the key of the guide is positioned in keyway 474. Keyway474 only allows the use of expandable trial 460′ with the appropriateguide. When expandable trial 460′ is fully inserted in the first guide,an end of the guide release of the guide may extend into guide opening476 to inhibit further insertion of the expandable trial.

Rotator 464 may be located near a first end of expandable trial 460′. Atool may be positioned in rotator 464. Turning the tool may advance ashaft in the upper part of body 462. Torque needed to turn the tool andadvance the shaft may be offset by counter-torque applied to the handleof the bridge assembly. The amount of advancement of the shaft may beindicated on scale 466. Scale 466 may indicate height corresponding toheight between the upper portion of movable plate 470 and the lowerportion of base plate 468.

Turning rotator 464 extends the shaft against an actuator located in thelower part of body 462. The actuator may engage a linkage mechanismcoupled to base plate 468 and movable plate 470. The actuator may pushand move a linkage pin. The linkage pin is coupled to lifting arms. Whenthe linkage pin is moved, the linkage arms raise movable plate 470 frombase plate 468. FIG. 78 depicts an end portion of expandable trial withmovable plate 470 lifted above base plate 468.

Before insertion through passages of the guides, the movable plates ofthe expandable trials may be adjusted relative to the base plates sothat the movable plates and base plates can be inserted into the discspace between the vertebrae. The expandable trials may be inserted inthe appropriate insertion guides so that the movable plates and baseplates of the expandable trials extend into the disc space between thevertebrae. The base plates may be abutted against the end plate of thelower vertebra by loosening the knob of the bridge assembly and movingthe base plates against the lower vertebra. The knob may be tightened toinhibit additional movement of the expandable trials relative to thelower vertebrae.

FIG. 94 depicts expandable trials 460′, 460″ positioned in guides 478′,478″. The rotators of expandable trials 460′, 460″ may be turned in afirst direction to lift movable plates 470 above the base plates 468.The tool used to turn the rotators may include a torque gauge. Therotators may be turned until a desired amount of torque is applied. Whenthe desired amount of torque is applied, the height indicated on scales466 of expandable trials may correspond to the heights of dynamicinterbody devices to be implanted between the vertebrae.

The appropriate dynamic interbody devices may be selected from theinstrument kit. Each dynamic interbody device may be coupled to anappropriate inserter. The rotator of first expandable trial 460′ may beturned in the direction opposite to the direction that lifts movableplate 470 from base plate 468. The grip of guide release 482 of firstguide 478′ may be pulled and expandable trial 460′ may be removed fromthe first guide. The vertebrae may be prepared to receive the firstdynamic interbody device. For example, a channel may be formed in avertebra to accept a keel of the dynamic interbody device. The firstdynamic interbody device may be inserted through first guide 478′ andinto the disc space. The same procedure may be followed to insert thesecond dynamic interbody device into the disc space.

The portions of the inserters that fit in the inserter openings of thedynamic interbody devices may be retracted from the inserter openings.The portions of the inserter that reside in the curved slots of thesecond members and third members of the dynamic interbody devices may berotated to remove the portions from the curved slots. The inserters maybe removed from the guides 478′, 478″. Tap connectors 522 may bereleased and removed from taps 458. Support frame 542 and instrumentguides 478′, 478″ may be removed from the patient.

Taps 458 may be removed from the vertebrae and bone fasteners of dynamicposterior stabilization systems may be inserted in the openings wherethe taps where positioned. A length of a dampener system of a firstdynamic posterior stabilization system may be adjusted so that thedampener system can be coupled to the bone fasteners. The dampenersystem may be secured to the bone fasteners to form the first dynamicposterior stabilization system. A length of a dampener system of asecond dynamic posterior stabilization system may be adjusted so thatthe dampener system can be coupled to the bone fasteners. The dampenersystem may be coupled to the bone fasteners to form the second dynamicposterior stabilization system. If needed, a cross link may be coupledto the first dynamic posterior stabilization system and the seconddynamic posterior stabilization system.

In this patent, certain U.S. patents, and U.S. patent applications havebeen incorporated by reference. The text of such U.S. patents and U.S.patent applications is, however, only incorporated by reference to theextent that no conflict exists between such text and the otherstatements and drawings set forth herein. In the event of such conflict,then any such conflicting text in such incorporated by reference U.S.patents and U.S. patent applications is specifically not incorporated byreference in this patent.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as examples of embodiments. Elements and materials maybe substituted for those illustrated and described herein, parts andprocesses may be reversed, and certain features of the invention may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims.

1-20. (canceled)
 21. A dampener system for stabilizing a portion of ahuman spine, comprising: a fixed length elongated member, wherein theelongated member comprises a first portion configured to couple to afirst bone fastener, a second portion having a first diameter, and athird portion having a diameter less than the diameter of the secondportion; a dampener set coupled to the second portion of the elongatedmember; and an offset member coupled to the elongated member, the offsetmember configured to couple to a second bone fastener.
 22. The dampenersystem of claim 21, wherein the offset member comprises a frame.
 23. Thedampener system of claim 22, wherein the elongated member comprises afourth portion having a diameter larger than the diameter of the thirdportion, wherein the third portion is located between the second portionand the fourth portion.
 24. The dampener system of claim 23, furthercomprising a first washer positioned on the third portion of theelongated member adjacent to the second portion, a second washerpositioned on the third portion of the elongated member adjacent to thefourth portion, wherein the dampener set is positioned between the firstwasher and the second washer, wherein an opening in the first washer issmaller than a diameter of the second portion and larger than a diameterof the third portion, wherein an opening in the second washer is smallerthan a diameter of the fourth portion and larger than a diameter of thethird portion, and wherein arms of the frame are positioned on oppositesides of the first washer and the second washer.
 25. The dampener systemof claim 21, further comprising a plate having an opening sized largerthan the third portion of the elongated member and smaller than thesecond portion of the elongated member, wherein the third portion ispositioned through the opening.
 26. The dampener system of claim 25,further comprising a guide coupled to the offset member and the plate.27. The dampener system of claim 25, wherein a portion of the dampenerset is positioned between the offset member and the plate.
 28. Thedampener system of claim 25, further comprising a second dampener setpositioned between the plate and the offset member.
 29. A dampenersystem for stabilizing a portion of a human spine, comprising: a fixedlength elongated member, wherein the elongated member includes a portionconfigured to couple to a first bone fastener; a first stop coupled tothe elongated member; a second stop coupled to the elongated member; afirst dampener set positioned on the elongated member, where travel ofthe first dampener set on the elongated member is limited by the firststop; a second dampener set positioned on the elongated member, wheretravel of the second dampener set on the elongated member is limited bythe second stop; and a member positioned between the first dampener setand the second dampener set, wherein the member is configured to coupleto a second bone fastener.
 30. The dampener system of claim 29, whereinthe member comprises a sleeve.
 31. The dampener system of claim 29,wherein the member comprises an offset member.
 32. The dampener systemof claim 29, wherein the first stop is a first arm of a frame and thesecond stop is a second arm of a frame positioned on the elongatedmember.
 33. The dampener system of claim 32, wherein the elongatedmember comprises a reduced diameter portion, wherein a pair of washersare positioned are positioned on the reduced diameter portion of theelongated member and openings of the washers are sized to inhibit travelof the washers to other portions of the elongated member, and whereinthe first dampener set is positioned between the pair of washers.
 34. Adampener system for stabilizing a portion of a human spine, comprising:a fixed length elongated member, wherein the elongated member includes aportion configured to couple to a first bone fastener; a frame coupledto the elongated member, wherein the frame includes a portion configuredto couple to a second bone fastener; a first dampener set coupled to theelongated member; a second dampener set coupled to the elongated member;and a slide coupled to the elongated member between the first dampenerset and the second dampener set.
 35. The dampener system of claim 34,wherein the first dampener set is coupled to the frame and the elongatedmember is positioned through the second dampener set, wherein the slideis configured to compress the first dampener set against a first arm ofthe frame, and wherein the slide is configured to compress the seconddampener set against a second arm of the frame.
 36. The dampener systemof claim 34, further comprising a washer positioned on the elongatedmember between a bottom of the frame and the first dampener set.
 37. Thedampener system of claim 36, wherein the elongated member comprises afirst portion having a diameter larger than a diameter of an openingthrough the washer, a second portion having a diameter smaller than thediameter of the opening through the washer, and wherein the firstdampener set is positioned on the second portion of the elongatedmember.
 38. The dampener system of claim 34, further comprising a stopcoupled to the elongated member above the second dampener set.
 39. Thedampener system of claim 34, wherein the portion of the frame configuredto couple to the second bone fastener is in-line with the elongatedmember.
 40. The dampener system of claim 34, wherein the portion of theframe configured to couple to the second bone fastener is offset fromthe elongated member. 41-147. (canceled)